This is an odd behavior that I noticed.

I created a 100x100 white canvas. I added a new layer, then I used a pixel brush with size 1px, selected the rectangle tool and drew a rectangle. Then I created a clone layer and added to it a transform mask by right clicking on the layer, then Add and then Transform mask. So far so good. I finally I clicked on Transform a layer or a selection while on the Transform Mask layer. I pressed shift and rotated it 180 degrees and moved it down. Now this is when the issues start.

1) If you try to move the transform mask of the clone layer the bounding rectangle moves at a different speed relative to the drawing. The bounding rectangle looks correct but the drawing seems to move about twice as fast and it can get out of the bounding rectangle.

2) Once you stop moving the rectangle(and press enter) to accept the new position, if you wait a few seconds the drawing on the clone layer will jump in position slightly, about a pixel. This happens no matter where you move it.

3) In this particular scenario another line appears magically to the left of the original rectangle in the original layer. I don't know if the previous point relates to this one.

This behavior is quite annoying since lately I have been drawing playing cards and when trying to align both ends they end up jumping slightly and messing with the alignment.

Here is the example .kra so others can see what is happening: https://mega.nz/#!xjJSRahD!zpjZqsJ-bF1K ... IPtWgcKL64

I installed krita on KDE Neon and the version of Krita is 4.2.8.

Can you try the Nightly Build appimage from here: https://binary-factory.kde.org/job/Krit ... age_Build/
There are problems with the KDE binary factory appimages and you may have to download it as a document (which takes a long time) and then do File -> Save Document As.

There have been several transform bugs that have been fixed recently so the latest nightly build may fix your problem.

Having said that, it does sound similar to this bug: https://bugs.kde.org/show_bug.cgi?id=415788 which hasn't been fixed yet.

Also, there is a problem with the KDE Neon package: https://bugs.kde.org/show_bug.cgi?id=416750 so you may want to consider running the 4.2.8 standard appimage anyway, which is available from the normal krita download site.

I tried downloading the file named krita-4.3.0-prealpha-ba4e484-x86_64.appimage and just ran it once. I opened the file I had created and tried moving the mask transformation.

I noticed three things.
1. It no longer shows a bounding rectangle when moving it but the movement seems to be twice as fast(as in I try to move it one pixel to the right and it instead moves two).
2. After the movement stops and I wait a few seconds the image again jumps a pixel to the left.
3. After the jump I notice the artifacts still(maybe a line on top or a line to the left)

I would say those bug 415788 seems to be basically the same problem. Also thank you for mentioning 416750, I had exactly that issue but I wasn't sure if I was going crazy or not. Now I know its related to the version of Qt 5.13. Thank you for your quick reply.