Actually, that exact thing happens when you don't format system.
graham- Did you do the following before installing the rom?
1)wipe data/factory reset
2)wipe cache
3)wipe dalvik cache
4)format system
If not, I would go back and do exactly those steps, then reflash the rom.
Also, be sure you are on the 173 system, and not 748.
Originally I did do all of that. I just tried again with the same result. Also I tried with the Eclipse rom which also nets the same thing. Looking at the settings here's what I got.
System Version - 6.12.173.XT912.Verizon.en.US
Android Version - 2.3.6
Baseband Version - Unknown
Webtop Version - WT-2.0.0-69-DHD_TA-1
Kernel Version - 2.6.35.7-ge88eaad
w30471@il93lnxdroid42 #1
Build Number - RazrX_V1.2
ERI Version - Unknown
PRL Version - Unknown