We study Banach spaces over a non-spherically complete non-Archimedean valued field K. We prove that a non-Archimedean Banach space over K which contains a linearly homeomorphic copy of $l^{∞}$ (hence $l^{∞}$ itself) is not a K-space. We discuss the three-space problem for a few properties of non-Archimedean Banach spaces.