Since you are upgrading from a rather old version of the controls the described rendering issues are expected. Note that we are doing our best to improve the feel and the look of our controls with each and every release and this is the reason for suggesting slightly updates to our customers. In your case the migration us rather big and the changes in the control appearance is more than expected. However, you are able to override the built in styles or even create your own.
Here are some references that might be helpful:
1. How skins work
2. Creating a custom skin
3. Modifying existing skins/creating new skins
I hope this helps.
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