I've just upgraded to ThinkGeo.MapSuite.WmsServer V11.0.0-beta002 and this issue has resurfaced.
You'll see in this discussion thread that MapSuite repaired this issue in WmsServerEdition V188.8.131.523.
You'll recall the original issue was that after the timeout period (5 minutes) the issue was present. With WmsServer the issue occurs all the time (inside and outside the 5 minute timeout window).
Please let me know what you find.