Oh yeah, I had forgotten about that. As I recall, they started doing that right after they moved to TMR2. It didn't last too long either. Some of the tones sounded downright fierce when converted to digital.
I'm quite certain it was a technical reason why they started doing that, and not an operational reason. The paging receivers would've still been analog VHF. Maybe it had something to do with the bridges they were using between the new and old systems.