That’s the first thing I checked.
However, in the meantime I did discover the problem. I’ve been recycling projects like this for several years now, but this issue has started only recently, so I suspected C7.5. I opened the project in C7 and did the same export and both QuickTime and Soundtrack Pro agreed with Cubase. So it’s definitely yet another C7.5 bug. Unfortunately I destroyed the possibility of a repeatable test by saving the project in C7. The next time I opened the project in C7.5 and did the export it was correct.