I have observed what may be this same bug in WSPR and FST4(W) transmissions: The radio will go into transmit, but no audio will be produced.
An important clue: If one has CWID enabled (I have it set to 1 minute) the CWID will occur at the beginning of the transmit period - and then nothing else, implying a sequencing issue in the code that was not present in a previous version. This bug is very annoying in the longer (300, 900, 1800) second modes!
If one is quick, one can toggle the "TX Next" button and/or the TX enable button and cause the transmission to occur normally - but this his hit and miss.
Eventually, transmission will commence normally on subsequent TX periods.