[Simh] Strange VMS 4.x-related bug

[Andrew Warkentin]

I have tried to run VMS 4.4 and VMS 4.6 under the VAX/11-780 simulator. 
It boots properly every time without the mandatory update installed, but 
it hangs after the system version have been printed on the console the 
first time it is booted after the mandatory update has been installed. 
If it is rebooted, it boots properly, but it continues to alternate 
between hanging and booting properly on successive boots. I am not sure 
if this is a SIMH bug, or if I have misconfigured VMS (but I just went 
with the default install and did not change any configuration). It is 
kind of weird that it starts hanging only after the mandatory update has 
been installed. VMS 3.0 (in the VAX-11/780 simulator) and VMS 6.2 (in 
the MicroVAX 3900 simulator) boot properly every time.