switching configs doesn't cancel previous-config's tasks

when i switch rapidly between my many configurations, to compare them, to update them, to ensure they're correct etc, each time i switch a new task is spawned for "parsing C++ files" and possibly others, yet the one(s) it was PREVIOUSLY doing don't get canceled. This ends up consuming an insane amount of CPU eventually bringing the entire app to a halt, forcing me to kill the process.  see screen shots.