Hello,
In my current project with some layers and some very basic pixeled drawings it happens. First how to reproduce
Make a project with a layer and draw some random pixels.
Press S to select rectangle selection and select some of the pixels.
Press M to move the selection.
While pressing CTRL (move more than 1 pixel each arrow button) press an arrow, and here it happens, what you are moving is actually a copy of the selection and you are not moving it.
When not using CTRL for the first pixel there is no problem.
If you can't reproduce it i can maybe send you the current PDN.
Thanks