WPF, Thumb cursor of GridViewColumnHeader not changed in custom control when resizing?

Simplely derived from GridViewColumnHeader without styling,

class SampleHeader : GridViewColumnHeader {}

and use it like:

<StackPanel Orientation="Horizontal">
  <SampleHeader Content="Col1" />
  <SampleHeader Content="Col2" />
</StackPanel>

Very simple, but in runtime, the thumb cursor will not change to resizing cursor.

I try to use the standard one, it works correctly, now i had to run a dummy once to make the correct resizing cursor fired in SampleHeader.

Is it a bug or else ?