Tryndamere's Undying Rage can be used when in Guardian Angel stasis.

I was in a ranked game and it was coming down to the final fight, I died before I could get my ultimate off as Tryndamere and I went into Guardian Angel stasis, but I kept on pressing R and it went off when in the stasis, so the entire duration of the ult went off when I was in stasis. This was pretty game breaking as it was definitely one of the reasons we lost. Could anyone tell me if this interaction is intentional or not? I looked it up and couldn't find anything. Thanks.