What I neglected to tell you all was that in the autoexec macro, we run a routine which updates references libraries (this is because our client does not seem to have a standard machine config). One of the references is to DAO and we programatically remove and re-add the references to DAO each time the mdb is opened. This was the culprit.
I have no idea what the delay occurs in closing the form and not opening the form. Sourcesafe was a red-herring - for some reason startup appears different under sourcesafe than if the mdb isn't under source control.