If TXID (and RXID, I suppose, though it shouldn't have an effect) is turned off, and I toggle T/R, I see fldigi TX something at the beginning and the end. I don't have anything in the TX pane to send.
It seems to send something, then a bunch of nothing (expected, because there is naught to send), then when I toggle T/R off, fldigi sends another brief "something".
73 Rich NE1EE
The Dusty Key
On the banks of the Piscataqua
Rich NE1EE