Graphic issues with WPF are not uncommon at all. This may be partially due to graphic card drivers having varying effects with hardware rendering on WPF applications . The same application may look different on PCs with different hardware specifications. In our situation, we had an image rendering with jagged lines on a couple of PCs, and looked fine on others.
In order to troubleshoot if it’s a hardware problem, or your code, I find that the simplest approach is to first disable hardware rendering on your machine, by modifying a registry key. That registry key might not be on your machine, so add it if it isn’t. By default if that key is absent, WPF assumes hardware rendering should be enabled.
After you reboot, and the graphic problem has disappeared because your PC is now using software rendering, you know for sure that your code is fine. Next you will have to update your graphics card driver, computer bios, and make sure you have at least .NET Framework 3.5 SP1 installed.
Here’s a link for Guidelines for troubleshooting graphic issues on WPF. It’s quite useful, and covers what I discussed above. Give this a go, it has helped identified our graphics problem very swiftly.