macduff,
I know this is not the answer to your question, but thought maybe it might help someone.
When we started the PDM system, I checked into the PDM 1874 files. I never deleted any files from my working directory. Opening a drawing of a small part, would take about 7 minutes. My VAR responded by saying that, “I should delete any unused files in my working directory”. I have done this ever since and had no problems since. If someone comes to me and wants me to open an assembly drawing from the PDM I will either move my working directory or put the newly opened files somewhere else. I never mix projects anymore. The theory behind this as I under stand it is that PDM will compare each file you are opening with each file in your working directory, which takes time.
Bradley