Audio delays in exported tracks using racks

[jamesridge]

Last night I was bouncing down a mix session using "export->create audio file". The exported file sounded great except for the vocal tracks I had running through a rack to another track for use as a reverb send; they were no longer synchronized with the other tracks. I understand the problems with some plugins and delay compensation (I was using SIR) but it played perfectly. The problem was only on export. Any ideas?

Thanks,
Jay