I described what may be the trip wire which lends to the condition. It may be a false cause.
I am perfectly capable of continuing to work with the tabs as uncloseable. It does mean that over time I will probably accumulate more tabs in the SQL Editor than is practical.
Sometimes, or often, in order to keep the number of tabs down, I will paste in another PL/SQL into the tab, compile it, and now the unclosable tab is now supporting a different procedure. (This is not comfortable to do, but I have done this often enough it should not be uncomfortable.)
Once we have tripped the uncloseable wire, if I open a new blank tab in the SQL Editor, that tab is permanently open.
I always operate with 3 SQL Editors going. When the uncloseable trip wire happens, it is only the 3rd SQL Editor which has this behavior. The SQL Editor, by the way, cannot be closed either. It will prompt me about any tabs with unsaved content, but it still will not close the tab. Meanwhile, the other 2 SQL Editors, if I were to close their tabs, they do so just fine.
Quite often, the 2nd SQL Editor has several tabs opened with a local *.SQL file. Never a problem. So, this relates to the PL/SQL Procedures in some way.
Not every time the computer goes to sleep does it trip the closeable wire. It is not 100%. Often enough to think in those terms, but there are exceptions when it did not.
As I said, this has been going on for several releases now. I never said anything because I figured someone else was making the case and eventually, the new Toad Releases would have some fix. I am a pretty bland guy. Enhancements are just bloat ware to me. Team Coding just means that the very first time after you have restarted Toad, that you close a tab, that TOAD is going to protest with [Control ‘dp Team Coding’ has no parent window]. OK to that and I will not seem Team Coding come up again until I have shut down Toad and brought it back up and then closed that first tab.