I made a video explaining what happens.
when i leave the game window in the unity 5.2.2 editor - the mouse curse which is hidden in the game - stays hidden. it didn’t happen in unity 4
is this a bug in unity ? was it reported already?
This often happens to me on v2017.2.0xb6 Linux Personal, but worse, afterwards the mouse is completely invisible in the Inspector panel following a Play preview and sometimes other panels too. I can only stop the Play preview with ctrl+p.
To get the cursor back in the Unity UI I must reset the overall layout: Window > Layouts > *preferred layout name.