Bug 1 FRAME animation clip results in a length of 1 SECOND in Animator

I have several animation clips with a duration of 1 frame. The importer is set up properly, and the preview window for the importer shows the clips correctly. (For example "CanopyOpen" runs from frame 429 to frame 430 and looks correct in the preview window.)

However, the Animator thinks some of these clips are 1 SECOND long. In the Animator state window, if I click on the transition to that clip, it shows the clip as 1 second even though it should be 0.033 seconds. Additionally, the preview window for the Animator shows the clip at the incorrect 1 second duration.

(We are veteran devs, so we've checked most of the obvious stuff. .meta file data for the .fbx looks correct, no time scales applied, etc, etc.)