WPF visual problems on Windows XP

Question

We have a huge project in WPF .NET 4.0 which should support Windows XP SP3 and above. (hence the use of .NET 4.0) It has no problems whatsoever on Windows 7 and 8/8.1. However we're experiencing major visual issues when running on Windows XP to the point that the application is unusable.
I searched a lot and came across some similar questions such as this one but none of the suggested solutions worked for us.
Here's an screen shot taken on Windows XP SP3:

The odd thing here is that there is clone of "28" TextBlock you see in the screen shot, to the left of it. They have everything in common except their name but the left one is not rendered properly!
And here is how it really looks like (taken on a Windows 8.1 test machine):

Some pages are even worse:

When I remove AllowsTransparency from the main window, it looks like this on XP: (Note that the title bar has no problems any more)

We're really stuck and have no clues about its cause. Any help would be appreciated.

Answer 1

It seems this problem is related to the graphic card. In another VM with a different graphics accelerator we didn't face any major problems. In the problematic test machine, we lowered hardware acceleration to the third level and the problem is gone.
Display Properties -> Settings -> Advanced -> Troubleshoot

Although there are still some small issues with some mouse over animations and we lost the benefits cursor accelerations bring to the table, it's acceptable for us since not much is expected from Windows XP.