Before to report this to wordpress I would like to know if it's just me or it's actually a bug. I noticed also another user that asked on the wordpress forum but he hadn't an answer for that: https://wordpress.org/support/topic/admin-left-menu-overlap
It happens almost every time I move the cursor above the panel and it seems to give this problem only in Chrome but I couldn't try it in other browser except for Edge where it seems to work fine.
My environment information is:
OS: Windows 10 64bit
Browser: 45.0.2454.78 beta-m (64-bit) extensions all deactivated