Question about Warmogs.

Something I noticed a bit recently regarding Warmogs. The passive says that if you don't take damage during the last 8 seconds you get higher health regen(can't remember numbers off hand). Does having a shield on affect this? Because I've noticed that the 8second timer on the item slot does not reset when you get damaged but you have a shield on and the damage doesn't go through the shield, however the regeneration doesn't seem to kick in till after another 8seconds has elapsed, so the timer will be turned off showing that it's active but the regeneration hasn't increased.

Hope this makes sense, and if anyone could let me know if there's something here that I'm misunderstanding or if this is a bug, thanks.