GPRS/Data only starts after reset I have Karbonn A9, Android 2.3.6.
The GPRS/Data does not switch on occasionally, but once I reboot the phone I can start it. 
After deactivating GPRS/Data I have to reboot the phone get either data or GPRS to connect again. What could be causing this?
Backup your data and factory reset your device. If problem is intact, its firmware issue. Fixing it isn't easier than flashing new ROM.

The best way to work around: Disconnect Mobile Data by renaming APN. No need to factory reset or to flash new ROM. You don't need to rename APN manually. Install Widgetsoid and use its mobile data toggle widget. In settings, make sure toggle method is APN renaming. Done!