On Truckers Edge and Express there is a bug that prevents the ability to change truck type between General and Specific.
If everything is deselected from the truck types drop down menu, when you move between General and Specific buttons, you are unable to select a truck type from the drop down menu.
For example: If you are on General, and there is no truck types selected, then when you click on Specific and try to add truck types it will force you back to General.
The resolution for this, is to simply select a truck type in the drop down menu, then change between General and Specific.
This bug is monitored using the Change Request:
1-2REWSUAY - TE and Express - Change request to monitor bug. If no truck type is selected in the drop down menu, then you switch between general and specific, when you click the drop down menu again it will kick you back to the previous general-specific selection.