Alright, storytime. So I was on my 19 twink a couple of weeks ago when I was spamming my Titanium Seal Of Dalaran and a rogue that was following me in the alliance tunnel randomly comes out of stealth and at the same time it said he caught it, now I thought this was just a bit of a coincedence and the rogue must have misclicked stealth, but I continued to test this anyway with my 70 rogue twink friend and I found that infact if someone in stealth catches the coin, it breaks stealth o:
Now, some may scream useless, but there's no harm in spamming the seal every 10 seconds and catching out the occasional rogue/feral druid (also tried with my 85 druid friend).
Here's a vid of me using it against my 70 twink friend in a duel and it breaking her stealth : 4.2.2 WoW Titanium Seal Of Dalaran Exploit. - YouTube
Note - it says "Titsandwich makes some strange gestures" because we're in a duel. When I did it in WSG it said the rogue had caught it s:
-Btw I am on Jubei'thos US
Edit : Just tried on a fellow horde while in a BG and it does not break stealth for friendly units.