I think the behavior might just be different than it is in XCode, which is what I'm used to.
I had the problem in the main PROGRAM unit when I tried to step into a toolbox call ('MoreMasters;' which probably isn't even necessary any more.)
When I tried to step into one of my own procedures, called in the main program but residing in another unit, it did successfully step into it, and with the expected behavior.
In XCode, if there's no source available for a call that you step into, it simply executes it and steps to the next line (as if one had used XCode's 'step over', instead. It's still jarring to think that I'll have to make sure I don't accidentally step into a toolbox call. I'm sure I'll get used to it.
Thanks for the reply.