Look in the FARs under "Logging PIC" and it will explain that you must be current and rated on the a/c.
Without an IR you are not rated to fly in cloud
QED
I first came across this during my IR training (and I think the oral), and never logged PIC and Actual at the same time. I'd hate for someone to go for the IR test, and get rejected by the examiner when they inspect the logbook.
I think it's also in Jack Lynch's FAA FAQ which was available on the FAA website. Its a big doc though and may take some time to find
If i find it, I'll post it...