There were some issues with assigning UIElements as column header, but it was fixed. The fix should be available in the Latest Internal Build which will be released later today. You will be able to get it from your Client.NET.
When the build is released, can you try to upgrade to its binaries and see whether the issue will be resolved.
In case the issue is not resolved with the Latest Internal Build, we would like to ask you to zip and attach your project and we will immediately take a look at it to see what is going wrong.
About the mapping between Text property and resource key :
Our LocalizationManager has some automatic logic to search for Text or Content properties and set them .
For more details on LocalizationManager usage please check here
the Telerik team