Using BSR Mode of 8255 with 8085
It is widely standard practice that the output enable of bi-directional/multifunction I/O ports is affected only by the contents of the output configuration / direction register, and not by any change to the data register.

You may think of the bit set/reset mode as being special, but all it is really doing is modifying the data register.  If unaltered, the output/input configuration remains as default, with port C split.