A little more feedback on this issue. I have reverted to using SDBG for the moment, despite the issue with the run control buttons, becaue I find it much easier to use, and apparently more powerful, when it stands alone. I presume there are ways to do everything I am accustomed to do when it is integrated with Plato, but it's easier in the hort term just to live with SDBG's new-found misbehaviour.
My purpose for posting is to say that it would be completely easy to live with this bug if it were not for another that I have just discovered. 😒hock: On the basis that all the three main run control buttons (Continue, Step Into and Step Over) have keyboard equivalents, in principle I just need to retrain myself to use them and to keep my mouse well away from the toolbar. Unfortunately, F6, F7 and F8 have no effect on my machine. Are they just supposed to work (my expectation), or is there a software setting, option or preference buried somewhere that needs to be frobbed?