Reboot after removing the iMate driver did not solve it.

Then I switched away from my wired mouse to the Apple wireless mouse than came with the Mac. Same problem.

A further data point: When I select an object to export, the dialog that comes up has the file named highlighted so you can begin typing the name of the exported file. This highlighting lasts from a second to a few seconds, but always "goes gray" as the attention of the program is drawn away. This occurs whether I have started to type, or just sat motionless after invoking export. It's as if the dialog box is suddenly "in the background."

None of these behaviors happens outside of MoI.

Curiouser and curiouser...