CP341 Coil Write problem

I'm having a very strange problem trying to set a coil over modbus on our Siemens CP341. Register reads/writes work; coil reads work; but coil writes are broken.

I have the following word, I'm trying to use the 8th bit to set/reset the coil:

When the 8th bit is 0, the coil write works fine, as seen in this modbus traffic capture:
That's me doing a coil write (fn 5) to coil 8, clearing it.

However, when that 8th bit is set, there are is nothing on the wire for that coil number. I'm baffled. Any ideas? Please don't assume I know what I am doing either. This stuff is brand new to me still.

Problem Solved

Rookie mistake, I suppose. To set a modbus coil, you must send 0xff00. The problem was I was trying to fit that into an INT, which doesn't work. Hence my coil sets never showed up in my modbus traffic trace. Changed the variable to WORD and now all is well.