Tahm Kench & Tryndamere skill interaction

[GAMEPLAY] - Tryndamere - While swallowed by - Tahm Kench's Devour[W] skill, Tryndamere can't activate his ultimate, Undying Rage[R], but attempting to will put it on cool-down.

This skill should be either one way or the other.

1. Swallowed and CAN'T cast Undying Rage[R]. (Not triggering cool-down)
2. Swallowed and CAN cast Undying Rage[R]. (Cool-down used and Tryndamere's ult duration begins in Tahm Kench's gut)

It is possible that Tahm Kench's Devour[W] skill is canceling Tryndamere's Undying Rage[R], but I never heard the Undying Rage[R] sound associated with it when it is activated, so I assume not.

This happened twice in one ARAM game, I can't test further as I don't have access to Tahm Kench.