I seem to remember there being a Chelon-themed Mahjong game available on Subeta, and I can't seem to find it. Has it been removed? Did I imagine it?

Are you thinking of Tubular Tiles? I joined the site a year and a half ago and to my knowledge it was taken down before then. (I didn't know it was Mahjong! now I really want to play it :P)

Tubular Tiles! Yes! Okay, so I didn't just imagine it. I wonder why it was removed.

it stopped working. i think it might have been flash-based?

Yes, I think they removed the Flash games when they wouldn't work properly anymore, though if I remember right, they are planning on finding a way to bring them back, they already brought back Spectrail.