I'm having the same trouble as Iain in bug #0001248 (Export Ranges problems)
I'm using Ardour2.11.1
I have 2 hours worth of stereo recordings in 4 tracks, when I export range markers the lengths of the audio files is correct, but the file starts at 0 of the session or possibly at the beginning of other ranges.
So for instance, if range 5 is 3 minutes 44 seconds, the exported file was the first 3'44" of the session, or possibly 3'44" starting at one of the other range start points.
If you need more accurate info I can sus it out some more. I'm really just checking to see if this is a known issue and (hopefully) I'm doing something wrong.