Whenever one has a corps in an area (or, whatever), and you select it for movement, an anomaly occurs: If, either while moving or when first starting out, the player decides to exchange factors with a garrison, the game switches focus to something other than the corps that was moving. However, it is still waiting for a move to happen. I think it's lost its mind at that point.
Anyhow, you have to re-select the corps in question to get it to move.
This is non-critical, since there's a really easy workaround. But, it may possibly indicate other issues, so I thought I would mention it.
(As you can tell by the flurry of posts, I played the game again last night.

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At LAST! The greatest campaign board game of all time is finally available for the PC. Can my old heart stand the strain?