Kalista + braum = forever no ult.

Hi guys! Was playing a ranked que the other day and my adc picked Kalista, so I chose braum for a nice ulty senergy. However, about 12 minutes into the match Kalista sucked me up to save me at a critical moment during my ultimate cast. My ulty remained off cool down but it wouldn't let me read the ability or activate it for the duration of the match. Thanks!