I just had a look at the Lepcha implementation (and improved it a bit on the way, Glyphs 2 will be help you with building components and feature code a bit).
Where are you testing? Indesign, MS Word, browser?
What did you use as names for the glyphs? The glyphs needed to the rightmost example in the second line should be: kha-lepcha, vowele-lepcha, consonantl-lepcha or uni1C02, uni1C2C, uni1C2F.
Can you send me your file that i can have a look.