I, too, ran into this problem in 15w51b. I logged into my world in Creative with the Elytra already equipped (and used, but not by much) and glided into my End portal. It worked fine, until I manually flew into the End gateway; then the Elytra stopped working entirely. Saving & quitting, then logging back in seems to fix it; but then I walked back into the gateway and it happened again.
Lily Aviarn
I, too, ran into this problem in 15w51b. I logged into my world in Creative with the Elytra already equipped (and used, but not by much) and glided into my End portal. It worked fine, until I manually flew into the End gateway; then the Elytra stopped working entirely. Saving & quitting, then logging back in seems to fix it; but then I walked back into the gateway and it happened again.