The short answer is that how SBUF is modified does play a role. The only reliable way to access SBUF is to use direct MOV's.

A write to SBUF loads the transmit register, and a read accesses a physically separate receive register. Using and instruction like ORL will cause something to happen. It will read the receive register, OR a value with that, then write the result to the transmit register. I can't think of a really good reason that you'd want to do this.