I've found a bug in the pre-alpha version of krita Git 199cd9f.

This is the bug: https://bugs.kde.org/407253

What should be the expected behavior?
Should the selection move to a new place or should it not be possible to be the selection?
Or maybe I am missing something

If you move the selection to an area with paint in it, it latches onto that area. The Contiguous Selection Tool has similar behaviour and will select other painted areas if you move the selection. They seem to have some kind of 'active engine' still working in them after the initial selection?