To fix a bug, you must be able to give a scenario to reproduce it.
Here all we read is that you probably have a permission error somewhere on your server.
You say that this is a bug in JMS but you don't describe any scenario and configuration to reproduce it.
If you want that we have a look on your server, you can always use our billable support at
www.jms2win.com/en/joomla-multisite?page...35&category_id=1
JMS is effectivelly sensitive to the hosting environment and when the permissions are not correctly managed by the server this may cause trouble to access the files and folders. We already tried detect several case that could cause problem and list them in the "check patches" screen but this is not easy and most people does not read the message displayed.