I've noticed this in both my Indian and Ottoman campaigns. Not only do mounted archers and gunners not fire on the move as they should, but also they don't skirmish anymore. So, basically like infantry skirmishers they are just expensive suicide troops and no use to anyone.
Personally, I'm rapidly having to rethink my strategy for units in ETW, simply because the historic army compositon can't be used as it should be. I'm even thinking of abandoning muskets armed infantry now simply because they refuse to react sensibly to local threats. It seems the only safe option is to build masses of swordsmen and zerg the whole battlefield.
Oh! BTW - Don't order your men to use their plug bayonets...apparently they don't know how to remove them again so it just converts them into expensive spearmen.
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