Bug or No Bug? (Coring Distance and Vassals)

[RMS Oceanic]

I thought the coring distance rules said you could always core a province next to a cored province of your vassal, but in this case the game seems to be ignoring that in favour of looking for seabound provinces of my own. Is that how the precedent is supposed to go, or is it a bug?

 

[grotaclas]

You can only core provinces which are next to your vassal if the province is on the same continent as your capital(I think the same applies to other subjects except colonial nations which follow different rules). Bitlis is in Asia and it looks like your capital is in Europe. That's why you can't core that province.