I'm happy to report that my initial post wasn't the result of hallucination- there is a way to streamline trimming but it uses the EXTEND command instead of TRIM- sounds kooky, but it works. Click on a line you want to trim on the side you want to keep, call the EXTEND command and click on the line you want to trim to and the excess line is gone- click away to clear the selection and trim again- the EXTEND command remains active. This is the behavior I originally asked about but couldn't recreate since I was using the wrong command. This method sometimes fails if the line to trim to offers a possibility to actually extend, but most of the time I'm trimming to a line that doesn't have an EXTEND option- can't explain why it trims correctly to a line through a circle, but I don't know what's going on in the code. After trimming this way for while it becomes really efficient- I make 2D drawings using MAKE2D and often have hundreds of lines the run on too far and trimming with EXTEND makes cleaning up a drawing much faster- for me at least.
Rick