Folding issue

I am experiencing a frequent but intermitten issue with PHPStorm code folding.  When I open a file and fold all the code (Ctrl Shift -), after a few seconds the code unfolds and the ability to fold is gone (the + / -  next to the line numbers are missing and the Ctrl Shift operations no longer work).  I have to close and reopen the file to get folding back.

Environment is:
Windows 7
PHPStorm 8.0.2
Files are on Ubuntu server with drives mapped using Samba

Has anyone else experienced this issue?