Two "Underground" tiles are incoherent in the editor. For example in the tileset editor, it says "Underground Ice", but when using triggers, it says "Underground Lava".
To clear all the problems with the underground tileset, here is a list of Underground tiles:
I hope this helps.'Gdrt' = Underground Dirt (cliff)
'Gbrk' = Underground Brick
'Grds' = Underground Red Stone
'Glvc' = Underground Ice Chunks or Lava Cracks in the trigger editor (and code)
'Glav' = Underground Ice or Lava in the trigger editor (and code)
'Gdkr' = Underground Dark Rock
'Ggrs' = Underground Grey Stones
'Gsqd' = Underground Square Tiles (cliff)
'cGc2' = Underground Dirt (non-cliff)
'cGc1' = Underground Square Tiles (non-cliff)
Edited by 3ICE: Shortened link by removing useless parameters. Not "All", just "Two" tiles. Not "mixed up", but "incoherent". Rewrote first sentence, removed old (wrong/misunderstandable) information, rewrote (new/fixed) information. Stickied forever.
Thanks to manstie for bringing it to our attention.