Tryndamere re-apples ult after it wears off. [GAMEPLAY]

In the new featured game mode a tryndamere was re-applying ult after it had expired. Sequence of events that happened twice. Velkoz versus Tryndamere

1. engaged trynd in lane while under tower
2. used full skill rotation E+W+Q+W+ult knocked him down to 10% hp, also hit him with 2 auto attacks (only 1 auto attack the second engage)
3. tryndamere activated ult and "E"'ed away from lane matchup.
4. I chased with q hitting him and slowing him while in lane away from tower waited about 4 seconds for his ult to wear of enough so I could ignite for the kill.
5. He "Q"'ed to heal momentarily then "E"'ed towards me and auto attacked once the second I would apply ignite. ON HIS auto Attack the words Undying rage toggled OFF then On again. He was then under the effects of ult for another 5 seconds and he killed me twice. Again he got 2 full duration ults.

This sequence of events only happened twice in game, I never fully laned against so I don't know if it was intentional or not. Later during the game his ult sequence and auto's worked normally. Also during these two sequences in discussion he never applied w once.

I dont know if this bug can be reproduced or not, whether or not its because of a new minion or item interaction.