I had this EXACT THING HAPPEN TO ME. IR film - I was like "does my camera have some weird leak? Why is the roll half developed on one side?" HAd it happen when testing, so the reel wasn't full, just a foot or so of film.
And I don't "invert" - I use Rodinal and do more of a "wine glass swirl" for 5 seconds. But anyway, I cut a piece of 3/4 PVC to hold the reel down (the lid closes and locks it in place) and also made a shorter one for 120, marked them both with sharpies. Problem solved.