data packet automatically activated on gingerbread 2.3.6
Install CatLog to check what's happening at the time of unlocking. Without logs, its hard to tell how to fix it.

Factory reset is the last option (not applicable if your firmware is broken).

If factory reset is unable to fix it or you don't want to do factory reset, install third-party apps which could turn off data by renaming APN. I'd recommend Widgetsoid for it. After installing it, add Data Toggle widget on homescreen &amp; choose APN Renaming as data toggle method from its settings. The bug can't by-pass it, for sure.