I keep using the "Station in a State" command to tell my army to wait somewhere. I look away, and seemingly at random, they're automatically moving back to the capital rather than staying put.
I can't figure out why they're doing this. There's no front lines nearby, the capital and state are both in the same HQ, and it seems like it occurs at random intervals rather than a set time.
If anybody can tell me what I'm missing or if they're having the same issue, please do. Preparing for a naval invasion, only to look back and see my army has decided it wants to move to the other end of the country, is driving me mad. When the army splits into multiple pieces as the ships ferry them, I can see groups leaving and moving back to the capital, breaking the transport order. Even the navy seems to do this sometimes.
Edit: Here's a link to the save if anybody wants to sanity check me. I unfortunately don't have the one from the start of the war where I split my army into ten stacks and you can see them each randomly leave Tohoku, but here you can see the 4th Japanese Army sitting around until Feb.16, then moving back to Kyoto unprompted. I've reloaded earlier saves and he's sat there for random times, even until May. This save has it consistently happen on Feb 16, though I can't tell why.