There is also one weird situation with pony camps.
I presume that all experienced players always build this camp close to base, so dwarven guardian battalions could be fast combined with ponies. ( Effect is that ponies with dwarves leave map before you combined new dwarven battalion with new pony set) But once I played Helm's Deep map, so I built pony camp at farthest corner of map, and near camp I summoned that Moria gate building so I can bring fresh battalions. First bug was that combination of ponies and dwarves always walked over Hornburg's wall and went in that corner of map. I always combined new battalion of ponies and dwarves before previous disappeared from map. So second bug was that no single Veteran units came back, I continued to combine and send them and in one moment I gave up.(Sent about 20 combinations) And few moments after last pony&dwarf unit disappeared from map, 6 battalions of Veterans appeared! So there is some side effect, and you should always wait that combined battalion disappear from map and then combine and send new one.