Middle mouse button on Linux systems is usually mapped to paste. Linux users are used to this functionality for pasting text, but most software disable it on other contexts. For example Blender does not paste the object on the clipboard when one pans the view.

Inkarnate currently pastes whenever the middle mouse button is pressed, which means a stamp gets pasted whenever the view is panned. One workaround is to use the space+mouse to pan, but that is much more inconvenient compared to pan using the mouse wheel which is standard in most software.