The 737 NG pressurisation controllers are pretty simple in their logic, if you select a low flight altitude and climb, the system will try to maintain a constant cabin altitude after climbing. Come on A340AM, please at least make the effort to look in the books, they explain it pretty nicely how the system works and what it aims to achieve (although not in detail what happens if you dont follow procedure and climb 8000ft above the selected FLT Alt). The manual states that deviations from the selected FLT Alt may cause the delta p to vary, descent mode will engage at 0.25 psi differential change, but if you climb above the selected altitude you can expect an ever increasing differential pressure.