I suspect the issue you are experiencing is related to the way
that the Tx signal is generated for the latest GFSK modulation
method used in FT8 and FT4. The signal is generated ahead of use
for the whole period whereas before with plain MFSK it was
generated on the fly as the transmission goes out. We need to
check that the signal is regenerated for the newly selected audio
offset, probably a minor omission in the code that triggers the
frequency shift.
