There's an old bug with Trojan healers, which was already present in original Settlers IV and still persists in History Edition. In short, they are slacking off. If you lead bunch of other wounded soldiers (e.g. Vikings) to their healer building, they approach it one after another and they all get healed after a while. Trojan soldiers also try to get healed and approach the building, but the healer doesn't come out more often than he does. It's not uncommong to leave ten wounded Trojan soldiers near the building and ten minutes later only one or two are healed.
Video: http://web.hisoftware.cz/sob/tmp/s4-trojan-healer.avi [13MB]
The video shows typical scenario. At 00:06, first bowman moves towards the building, reaches the spot at 00:12 (notice how he immediately takes one step away) and nothing happens. At 00:30, second bowman tries the same and fails completely. At 00:54, swordsman takes a chance, reaches the spot at 00:59 (also immediately steps away, but it's less noticeable), and the healer doesn't care either. Now sometimes, it's possible to select the soldier, quickly move him little bit closer to the building (I do it at 01:04) and he finally gets noticed by healer. It sometimes works and sometimes doesn't, I'd say the success rate is about 50%.
I'd really like to see this fixed.
No problem with higher priority stuff, I've been waiting for years, it doesn't have to be tomorrow. Next week is fine.
But seriously, check how it's done properly:
http://web.hisoftware.cz/sob/tmp/s4-viking-healer.avi
http://web.hisoftware.cz/sob/tmp/s4-mayan-healer.avi
One after another, approach and get healed, approach and get healed, ... like a clock. I don't have Roman save right now, but it's the same.
My guess is that it's because Trojan building is slightly larger than others and some "trigger area" which soldier must reach for healer to come out may not be large enough (or it may be partially covered by the building).