Hello - we have pretty much the exact same problem here at our organization. We are ready to deploy office 2010 and this problem is going to really hurt us - we have one form where there are multiple PDF exports and this of course is crashing infopath. In addition my pdf gets passed over to a fax server which errors because the infopath process has the file locked.
I downloaded and applied Office 2010 service pack this morning and it does not address this issue. Went through the service pack docs and they did not even address infopath. Sorry but that aint good enough Microsoft.
I am going to try to setup Office 2010 without infopath and see if I can install Infopath 2007- so everything other than infopath will be 2010 and infopath 2007. Not terribly optimisitc that it will be successful.