Woespike - Does it work with 10% impale extend mastery?

I think there's a bug but I'm not 100% sure. I have 2x woespike rings, and when I take the 10% for all impales to extend mastery, I would expect with enough hit rate, that the largest impale I apply doesn't fade away until natural expiry.

My current setup is on my Wozbo character, I attack at least 4x per second, with perforate of duality. I would expect the ~ 60 hits per second to cause the largest impale to get (on average) 6 extra hits, which should take care of any stray hits from things like shock/ freeze shrines etc, but it always seems that the largest impale drops off after just a second or two.