Yes, you right. I have investigated a bit more about this particular problem in 6.3 (unfortunately is not the only one). As I said the problem has occurred since they have included the support of API version 1.10 and the IBUSPIN class.
For those having good grasp with Proteus API, I should say that with previous release (i.e. 6.2) when a VSM model had to drive a state on its output, a call to EVENT *IDSIMPIN::setstate (ABSTIME time, RELTIME tg, STATE state) was used. For example to drive a 8-bit bus a contruction like this must be used:
for (i=0; i<8; ++i)
outputs->setstate(time, tg, dout & (1<<i) ? TSTATE : FSTATE);
// dout is the byte to send into the output
Above approach was "time spending" because it required the output was written bit-to-bit (in above example 8 times).
With new IBUSPIN support a bus output may be written "at once" using the member function VOID IBUSPIN::drivebusvalue (ABSTIME time, DWORD value), where the DWORD value is the bus value to be in output.
You can easily understand as this approach adds terrific speed and further efficiency to digital simulation. So, Labcenter has modified most of primitives model to accomodate for above described bus support.
However, this improvement did not achieve success for all primitives and for sure this is the case of digital MEMORY primitive. The 27256 model makes use of MEMORY_15_8 digital primitive and I verified that problem belong effectively to MEMORY primitive. For obscure reasons a digital word written onto the Address bus will not generate any event (or may be they are not simply registered in event structure) so it cannot raise for any output on Data bus.
I'm sure of what I say because I tested a single MEMORY primitive and I used LOGICSTATE Active object as digital address word.
I seen no output events will generated while simulating is on, but stopping simulation and run it again a new Data output will take place with a different Address word.
So, I agree that 6.2 SP5 is stable enough and is worthwhile to use it until all problems will sorted out. I dont uninstalled 6.3 from main partition but I have installed 6.2 SP5 on a different partition and created a further link to it. It looks it works provided that you change destination and working directory using link property and changing Path configuration in Proteus (set Path... option in menu System). The latter is required to address for old models and libraries. Doing so I can have 6.2 and 6.3 available on my desktop and I can switch over one of them just setting Path configuration.
Hope it helps