Ok guys after a lot of struggle I was able to update my wave to DDJF2 yesterday.
When I went there first time, the lady there updated it to DDJF2 but then after returning, I found out that the phone was going into debugging mode when I try to change some settings. Again went to the SVC and got it updated second time. And now its doing pretty good. I almost spent like 3 hours sitting there and waiting. Though the regional manager in my area helped me a lot.
But those multitasking issue still exist. Guys try this on your wave whetever may be your firmware versions.
Just keep homescreen running, no apps or widgets. Now open media browser and then minimise it by long pressing menu key. Then go to homescreen again. Then start music player and then minimise it again by menu key. Now see if the media browser is running or not. On my Wave the media browser closes automatically.
Case2 - Just keep homescreen running. Go to clock and then start stopwatch. Minimise it and start music player, minimise the music player and then go to task manager and see if the clock app is running or not. On my device it vanishes from task manager but it keep running when I manually start it again.
Pls test this on your wave and report back. I am not sure if I am alone facing these issues or its affecting all the devices ?