OK, I've found the solution to resolve the problem with Internet passthrough via ActiveSync 4.2. Tested and worked for me.
Here is what you should do:
1. Install/upgrade ActiveSync 4.2 if you haven't done so.
2. Download and unzip the attached file.
3. Double click LSPvalue.reg on your
desktop with ActiveSync 4.2 installed.
4. Click YES, then OK, and it's done!
Credit goes to Ghaled from the xda-developers forum for providing the fix. Details of the registry tweak are explained
HERE.