How does temperature affect buffer capacity?
If you follow this derivation of buffer capacity, the last equation shows you that buffer capacity is a function of $K_a$, so a change in the Ka will affect the buffer capacity. Also, since you know that $K_a$ is affected by temperature, that should lead you to realize that the actual chemical environment is different at different temperatures due to a different concentration of acid and weak base pair. The magnitude of effect maybe small, but your experiment can prove that one way or the other!