I've compiled Xfwm4 from GIT. I've noticed that Ctrl+F1 key shortcut (which is used for switching to first virtual desktop) causes that windows can't be freely moved or resized. Pressing Ctrl+F1 again fixes the problem, so: Ctrl+F1 - can't move Ctrl+F1 - can move Ctrl+F1 - can't move Ctrl+F1 - can move ... Only Ctrl+F1 is affected (AFAIK). The action doesn't matter, I can change it to something else like "show desktop" and the problem remains (but the action must be assigned to Ctrl+F1). The regression is caused by "Add PointerMotionHintMask" (0dfb55407a830572f03297b3c118fac1f3c5b80d) - reverting this commit fixes the issue.
Same issue here with xfce-base/xfwm4-4.13.0 on Gentoo.
Fixed in git, both branches (xfce-4.12 and master)
*** Bug 12677 has been marked as a duplicate of this bug. ***