Tainted Divine Teardrop not working as advertised

At first I thought it was broken altogether, because when used one it did literally nothing.
However after second try it seems that it doesn't work on EACH modifier - there is a chance (substatntial it would seem) that it does NOTHING for one or more modifier, which is NOT what it reads in the description.
I crafted a chaos bow and I chose to put +1 support skill gems not +2 and a mid tier Chaos damage over time multi because I was certain the former would flip between +1/+2 on every Teardrop use.