Unexpected behavior on WPF

Question

Hello,

We have a strange issue that occurs depending, apparently, on the computer configuration. 

In the attached file, you will find two screenshots issued from exactly the same code:

- Expected.jpg is the expected behavior of the window

- Unexpected.jpg is the unexpected behavior!  Why some parts are troncated?

For the above examples similar config are used (.Net 3.5 SP1). We tried several PC and we found out that on XP the expected behavior occurs but not on Vista. Is there any link? Why? 

More generally we have several cases where relative positioning of controls is incorrect, text in controls is clipped.

Thanks for your help,

Kamel