This risk did not exist with previous versions of the IDE. Prior to v18, each IDE kept correct track of its respective Arduino.
but to have multiple instances of the IDE up and running their respective code segments correctly connected to respective COM ports for the duration of the debugging session so that multiple sketches could be tweaked
Meanwhile, it appears the only solution is to have a separate computer for each Arduino. In other words, if you have three Arduinos, each with a different sketch, talking to each other over I2C or xBee, one must have three separate computers (Windows XP in my case), each running ONE instance of the IDE, with the three CRTs and three keyboards placed close enough to each other so the programmer can watch output on the three computer screens for the debugging and use the three keyboards for code tweaking.
Ordinarily one must use software from Microsoft or IBM to experience usage barriers like this.
It wasn't uberhund that I was quoting, so I don't think he's the one deleting posts.