Ok, this can have a *lot* of reasons.
1) Did you use the catel base control or do you use the behavior on a control?
2) Is the complete control reloaded by external components or layout restoring?
3) Are you using the latest beta?
4) I don't understand this:
Shouldn't that be DataContext? And... you can skip it, the latest version picks this up automatically.
If you create a new issue and upload the demo, I can take a look at it.