focus change with navigation callback

I need to have some function run when the focus leaves a certain 
text-input-pane. So I set up a navigation-callback for it, which just 
calls the needed function. It seems to be working fine, except that the 
focus doesn't leave the pane anymore. I don't want to control focus 
explicitly, I just want to restore the normal focus change behavior. How 
can I do that? How does the focus change process normally work? Is there 
a method I can specialize to run my function in addition to the usual 
process? Or is there a function I should call in my navigation callback?

Thanks,
Octav