If you bring up the Edit Spy Points window via Debug/Edit Spy Points from the Prolog console menu, there are three buttons in the upper right: Normal, Debug and Trace.
.
What do these buttons do? Pressing them doesn’t appear to be issuing commands to the Prolog engine that I can see.
They might not to much useful these days. I should check. Once upon a time SWI-Prolog was single threaded and they would control the debug mode (nodebug/0, debug/0. trace/0). These days the debugger runs in the pce thread and it is quite likely these buttons affect this thread, except that that doesn’t work as this IDE support thread runs in nodebug mode.
Possibly these should call tdebug/0 and friends.
Got it. Should I enter a bug somewhere to track?