Just recently my FCP7 has been importing files with the incorrect duration.
These are ProRes 23.976 files that, upon import, are displaying a duration that matches what a 24fps retime would play at.
For example, I have one 23.976 file that displays a duration of 2:02:49.61 in quicktime7.
When I import into FCP7 the duration becomes 2:02:42:00. The file still reads as 23.976 in FCP.
I exported this file through compressor as another ProRes 23.976 to make sure the original file wasn't corrupted. Same result.
I tried a wholly different video file this morning, only to see the same pattern occur.
In quicktime7 this 23.976 ProRes reads as 1:35:15.25
In FCP the 23.976 ProRes reads as 1:35:09:12
I know of this problem occurring in reference to audio files. I've heard of fixes related to changing the EasySetup. That fix has never worked for me. I've always changed the timecode metdata of the audio files in WavEditor. However, I can't make those kinds of changes on ProRes files. And even still, all the metadata indicates the correct timecode on the files. However FCP keeps altering the duration!!
What you think you are seeing is definitely not reverse telecine. Changing the speed of a file between 23.976 and 24.00 fps would be referred to as pullup or pulldown (depending on the direction).
But the duration readouts in Quicktime pro are notoriously unreliable. So it is hard to say for sure that the problem you are describing is actually a problem at all. You can try opening your clip in Cinema Tools and using the "conform" command to "force" your clip to 23.976 (it may just list 23.98 as an option ... they are actually the same thing, FCP just tends to confusingly round the numbers off).
Bring the file back into FCP and see if the duration is the same. In any case, you should trust the duration read-out in FCP more then anything that Quicktime Pro says. If you are not seeing any playback issues with the clip and it is correctly being labelled at 23.976), then what's the problem?