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- This article is about bugs in Scratch itself. For bugs in computer software, see Bug.
There are many notable bugs in Scratch. Some may just be graphical, some might impact coding, some might make text missing and some might show extra things.
Wrong Font Bug
In the Scratch 3.0 Paint Editor, sometimes the Sans Serif font displays as a larger Serif font. There is no known cause and solution for this bug, but the workaround is to use the Chinese, Japanese, or Korean fonts instead, as they all look very similar to the Sans Serif font.
No Last Post Bug
- Main article: No Last Post
In May 2017, when spammers were active, on some occasions the "last post" field next to a subforum description would be missing. Though it died down after a while, later changes to the forums seemed to bring it back. The reason why this happens remains unknown.
Disappearing Comment Bug
- Main article: Disappearing Comment Bug
Mainly found in Scratch 3.0, this bug causes profile, project, or studio comments to not show when attemping to view it. Sometimes, when the message for the comment is clicked, the comment section will not load. Then, if a user tries to view the page where the comment is without the direct comment link, the comment will not be shown. This can cause the inability to view, reply, delete, or report the comment. To fix this, do a hard refresh.
- Main article: Trending Glitch
Currently found in Scratch 3.0, the trending glitch is a way of getting one's project shown in the trending category of Explore without the project actually qualifying for "trending" status. Unsharing and then resharing projects utilizes the glitch by making the Scratch website believe that the reshared project received however many loves and favorites the project in question had before the reshare in a short amount of time when in fact the project had technically already had those loves and favorites before it was even shared. As a result, the project is shown as "trending."
Percent Custom Block
Found in the Scratch 3.0 project editor, naming a custom block "%" will result in Scratch not letting you press "ok." After pressing cancel, there will be a mass of random blocks at the top of the block palette. You must refresh the project to fix the bug.
As of March 2021, in Scratch 3.0, comments are sometimes duplicated. Sometimes, Scratchers will send 1 comment, and after posting the comment, see that they sent 1 comment, and leave the page.[clarify] Other Scratchers see it as 2 entirely same comments. This often results in Scratchers reporting the user and comment for spamming.
Automatic Logout Bug
X replacement Bug
Many Scratchers found out their projects' thumbnails became only a cat with a white background. This is seen in many projects and its reports are almost the most in all bugs. This bug reported on many topics and posts. This bug continously spread, until June 2021, this bug is still not fixed. It is a bug since May 2021. A simulation of this bug may be made within the animated project thumbnail set.  The exact cause is unknown but normally because Scratch is unable to load the image.
An unknown character (%15 for Unicode) put into a custom block makes strange blocks and sometimes even making a project's code unavailable but still works.
Disabled Keyboard Bug
This bug, seen only in Scratch 2.0, caused Scratch to not react to key presses, which impacted projects that needed key presses to work and meant that Scratchers could not program, due to most blocks needing to have words typed in them to work correctly. This bug was only seen with Firefox. There were, at the time, no ways to fix it forever, but it had been found that clicking outside Scratch (such as address bar) fixed it temporarily.
- Main article: Semicolon Glitch
Disappearing Text Bug
- Main article: Disappearing Text Bug
The Disappearing Text Bug was that text in some projects would disappear. It was seen in blocks with written text inside or dropdown menus. In some cases, only some text would disappear, but sometimes, almost all the text in the project would disappear. It has been fixed, and although it was reported to have appeared again in Scratch 2.0, it hasn't been seen for a few years.
Variables Not Fully Hiding
In Scratch 2.0, sometimes, variables did not completely disappear from the Stage when hidden via the checkbox next to its name. The exact cause is uncertain, but it is speculated that quickly switching costumes or backdrops caused it.
Speech Bubbles With Empty Space at the Bottom
ln Scratch 2.0, when changing to fullscreen, the outside of a speech bubble got amplified the correct amount, but the text appeared a bit smaller relative to the bubble. The result was that the speech bubble was a bit taller than it was supposed to be. This only happened with speech bubbles with lots of text, or large speech bubbles.
Broken Thumbnails and Profile Pictures
- Main article: Broken Thumbnail and Profile Picture Bug
As of June 2021, profile pictures and featured project thumbnails stopped showing. There were numerous posts about this on the forums. The bug started due to one of Scratch's subdomains, cdn2.scratch.mit.edu, being down. The downtime lasted 2 days, with any users trying to access images stored in it either getting a 500 Error, or getting a Guru Mediation error. After that time, the downtime stopped, however, the bug continued. After the downtime, many images were corrupted, so many images still could not load. It is suspected that Fastly being down has caused the CDN2 servers to wobble. During the downtime, many people attempting to change their profile pictures got them reset to the default Scratch Cat icon.
- The comment showed as "i just have to set clicks to XXXXXXXXXXXe+XXXXXXXXXX" but originally typed as "i just have to set clicks to 9999999999e+999999999"
- A project thumbnail like this project thumbnail is not the same image as the real project
- Chiroyce (6/11/2021). "Some project thumbnails have turned into Scratch Cat on a white background, and it still happens sometimes, unpredictably." topic:520710
- PrincessFlowerTV. (4/10/18). "The “Semicolin Glitch” was back, showing a semicolin at the bottom left of every page.[sic]" post:3059780
- Chiroyce (6/11/2021). "Some people are not able to change their profile pictures, and some profile pictures have turned into the default scratch cat silhouette, which is a huge problem, and it still happens sometimes, unpredictably." topic:520710