That is very odd, indeed... What modules do you have installed for DW? Either something changed from 6.11 to 6.12, or certain modules that are more dynamic (Workflow, perhaps?) keep a connection active even when a user isn't actually interacting with the page.
We have Task Manager, and so a little number displays above the "Lists" are on the main DocuWare web client page. I was thinking that number is dynamic, meaning the page can change due to activity elsewhere. But I just tested again, this time leaving DocuWare up in th ebrowser, and my license still timed out after 12 minutes.
BUT, the number of tasks in the list did not change during that time. Do you have something like Workflow, and is it active enough that little numeric indicators for tasks/lists are increasing? To put it another way, does every single thing on the page look the same as when you minimized it?
This is totally all just a shot in the dark... I do not know why your licenses would not be timing out the same way as they do for me. I hope Phil has some insights. If we every had licenses stay stuck, we would be in trouble as well, as I keep our number of licenses pretty tight (just 20 concurrent).