Hello David,
Finally I got to test the different Service Packs and the behavior is related to SP3. There is no themes or font smoothing. It is a basic bare-bones XP install. I get the same behavior whether I am using a Virtual Machine or not.
The application under test is a mix of C++ MFC and C# WinForms.
I implemented my "join" function by looking at the coordinates of the TextObjects and combining the ones that are contiguos (textObject1.Top == textObject2.Top and textObject1.Left + Width == textObject2.Left). It is still a hack but it works. It will be nice if this would not happen.
Regards,
Patricio.