Very welcome, August. "M" in prefix refers to a "member" - while number is an ID.
Btw, regarding your note "it only flashes for a couple of seconds when I regenerate." - you can always get to the full regeneration log by placing a mouse over the message area and RMB > Regeneration Log - it will open the window with full list of messages. Or like mentioned by Stefen read the trail file - it contains pretty much similar info (just more complicated to get to it among all other rows).
If you have assemblies that showed as fuly constrained in Wildfire and now report as having problems - please submit them to TS, this should not happen.
- Vlad