final hear from expert's analyse and opinion

this problem has been going on for some members here and me but still got have not got solution even from nokia, whether can be solve or not, this will be my last post on this 'memory full, close some application 1st' issue.... 'too tired'.....
Got my phone with this problem sent to nokia at 3 times, finally they change the whole board(as good as changing a new phone, got a new IMEI), on latest 3.04.37fm.
Bought a new 256mmc to treat my new phone, thinking that now i'm holding a new solid phone better than anyone else in the world. (also do not want the old mmc to corrupt the phone).
Load the card with fxeplorer, smart movie 2.73, some vid clips, some songs clip as ring tone. other app, later 1st, want to monitor the phone performance 1st. check the ' FreeMem: 6456kb' status, ok, satisfied.
Start using the phone(normal usage, like calls, sms, gprs etc) for about 9hrs, and BINGO! 'memory full, close some application 1st' when i want to show some vid clips to my friends in a pub.
Check the fexplorer, now it says 'FreeMem: 1078kb', tried compress memory, exit it, try open vid again, nothing move when click, tried fexplorer again, aslo cant open. Reboot the phone, now all goes back to normal.
The next day, load in a 'application manager', reboot and check, 'Free Memory: 6.64M', 'Running app: AppMan used 188k, Pinboard used 164k, Phone used 500k', killed the process of auto keylock and screensaver, and also Pinboard.
Go back to front page, now 'Free Memory: 6.8M', do a compress, now becomes 7.1M. And exit everything.....
Now open the Menu, Contacts, Log, make some calls and sms. Then exit everthing.
Open aplication manager again, 'Free Memory: 5.4M', 'Running app: AppMan used100k, Pinboard used: 164k, Phone used:500k, Menu used: 146, PhoneBook used: 240k, Logs used: 268k'. Killed all the processes, execpt, Phone and AppMan, as these cant be killed. Goes back to front page, 'Free Memory: 6.2M', do a compress and now 6.4M.
after some usage, do all over again, but after killing process and compression, the Free Memory figure will still get lower and lower, and finally gotta reboot the phone. in doing this, the phone can use longer before need to rebooting.
Don't understand why, the phone memory cant be freed completely when all app are closed and still appears in the 'AppMan's running process'. and even kill these process manually, still there is some memory cant be freed and accumulates until the message 'memory full' appears.
Anyone can analyse and explain, if my this long post is still not detail enough, please ask for more info, thankyou guys for your time in reading this......