setting SINGLESEG_OFF For HP-UX

Hi All, I need to pick your brains if possible. We have recently upgraded to IDS 7.31 UC2 on HP-UX 10.20 from 7.22 UC3 9 Big Jump I know ). But we have had a problem. We have two instance on the HP-UX box set up as follows :- 4 processors 4 Gig mem SHMMAX ~ 1G When we started the engines after upgrading one would start & the other would crash. We figured out it was to do with the amount of memory ( Virtual & resident ). We had to reduce the BUFFERS and SHMVIRTSIZE on both before we managed to start the engines up. The result is we 16M virtual segments being spawned off which not the case before and slower performance. Informix support have suggested that we set SINGLESEG_OFF=1 and then start the engines up. Now my questions are ( if anybody has come across this problem ) :- What major change have they made in 7.31UC3 that requires us to set this flag where as we did not have to before for 7.22UC3 ? What repercussions is this going to have , if any ? Cheers & thanks for your help in advance Pankaj