GateIn - Why can't custom portal see all skins?

This is a rather specific question to GateIn, but I can't get help anywhere else.

GateIn has a Skin Service which detects deployed skins automatically. This works fine for the defa开发者_运维知识库ult portal container, which correctly lists all available skins in the Choose Skin dialogue.

However, in other portals, such as the sample-portal or my own custom portal, only the default skin is listed. what do I have to do to get the skins displayed in all portals?

Thank you.