I can't reproduce this issue and I didn't receive any other similar reports.
I know the rotation feature is bugged and the problem manifests itself in more than one way. When I load a rotated map, its rotation is lost, but I don't get any error messages. Hopefully if I fix the rotation the whole issue will go away...
Might well be it, since the map I was saving and loading was rotated before editing. I needed that city to be on a southern coast and the river to run east to west...
Following up, yes, I can import unrotated maps (even with multiple edits) without problems. And with my workaround (Blueprint, Discard) I can get back maps that were rotated before saving.
