Bug with selection when pressing both RMB and LMB together: hold RMB on desktop and press LMB while holding RMB. You'll get file manager window. Close it and selection will follow your mouse while you're not holding the button.
I can reproduce with xfdesktop 4.13.2, I just need to press both RMB and LMB at the same time. The file manager is not opened anymore because gtk3 does not position the context menu under the cursor.
Created attachment 8366 proposed patch Same thing happens in Thunar also. My proposed change for xfdesktop is to stop an ongoing drag/selection event if the middle or right mouse button is pressed. Furthermore, this fixes a visual glitch (selection rectangle not being removed after right-clicking on a desktop icon).
Theo Linkspfeifer referenced this bugreport in commit 57ac5cb30a1e01bd506799a088940ca2e0f13ca0 Stop ongoing drag/selection if middle/right mouse button is pressed (Bug #14180) https://git.xfce.org/xfce/xfdesktop/commit?id=57ac5cb30a1e01bd506799a088940ca2e0f13ca0
Thanks for the patch, looks good to me. Can you also send one for Thunar?