QT FFT GUI - 3.7 works differently than 3.6

I’ve used the QT GUI Sink in ver 3.6 with good results.
In GRC 3.6 the Center Frequency (Hz) variable in the QT GUI Sink allows
inputting a value or variable that is added to the X-axis value display
when the Display RF Frequencies checkbox is checked. This in set in my
application to the NCO frequency of a digitally down-converting

In GRC 3.7 the QT GUI Frequency Sink display shows nothing when the
Center Frequency (Hz) is set to a value or a variable with a value well
above the actual baseband frequency (both QT GUI Sink and QT GUI
Frequency Sink work the same). The Display RF Frequencies check box does
nothing (does not alter the X-axis display, does not change the empty
FFT display).

Is there a bug in GRC 3.7, or has the behavior of Center Frequency (Hz)
and of the Display RF Frequencies checkbox been altered?

– Tom