Emnity-wise it does stack, but if you use it let's say back-to-back, the status effects are completely resisted.

Mobs gradually build resistance to it's effects overtime after each use, I think the first time the effects last 12 seconds, then 6, then 3, then completely resisted. I'm not TOO sure, but there's a time window when they are vulnerable to flash again.

It's the same for Shield Bash and Shield Swipe. Don't know if this is a universal thing though.