When I swap between my weapon bars my health drops. I'm not talking about losing it because of passive skills. My max health stays the same, but my actual health drops to 92% before returning to 100% after 4 seconds or so.
I removed all skills from both bars and with my tank gear my max health is 27,992, my health drops to 25,594 when I swap weapons.
I tried it with with my DPS gear and it doesn't happen.
I swapped out my shields for junk stolen shields my max health is 26,850 and when I swap it drops to 25,594. After more messing around I haven't found exactly what is causing it other than 1H and Shield on both bars. If I remove all gear except weapon/shield it doesn't happen, but my health is also about 16,000 at that point so not sure if it only happens when health is above some value (possibly 25,594)
Here is a video to show it off:
https://youtu.be/GMflIt2Up2o
While I was waiting for the video to upload I tried some more stuff. If I replaced both my 1H and Shield with stolen items, my health was 25,594. 27,992 is from the Hist Bark set 4 pc gives 1002 health plus 854 from enchantment. Bug seems to have something to do with a 4 pc Hist Bark. I'm guessing that even though both bars have the same set, it's losing the set bonus during the swap.