For what its worth. I have just tried a contest exchange macro in MMVARI:
DE $mycall$ 599 $serialnum$ $serialnum$ TU
$receive$ $endtime$ $log$
The K3 changes to RX immediately. An oddity I notice with MMVARI is at the start of a transmission there is about a seconds worth of diddles before the "message" is transmitted.
I normally use MMTTY along with 2Tone and GRITTY as additional decoders.
$call$ 599 13 13 $mycall$ $receive$ $endtime$ $log$
Changes to receive immediately.
If I call CQ it normally grows into a pileup and I use the following:
$call$ $call$ 599 $mycall$
$call$ tu $mycall$ $endtime$ $log$ up 1-3
What happens if you use a macro that doesn't log i.e. a previous serial number?
599 $serialnum-1$ $serialnum-1$ $receive$
Again these change to RX immediately. I backup the log every five contacts.