We have had an issue with published Seamless applications being unable to be restored/maximized after users have minimized them. The issue doesn’t appear to happen all the time but when this happens users were forced to logoff from the server and log back on to get back to working state.
The customer environment was XenApp 6.5 with published desktops and apps. Storefront used was 2.1
Cause – The source of the issue was the policy that was turned ON to ungroup the taskbar icons
Fix – Fix is to set the GPO that managed taskbar grouping to “not configured” or “Disabled”
In my case, the customer had this setting turned ON via Registry and I had to remove that to fix the issue. The below is the key that was turned ON and had to be removed.
Hope this helps somebody out there….
Citrixology 
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