strange multiplot behavior with wxt

I'm puzzled by a multiplot example where the output seems to be 
non-deterministic -- though the fault may be in my script 
(strange_multi.plt, attached).

I'm on Linux, using gnuplot 5.4.3 and also 5.4.8, using 
the wxt terminal for screen display with the command line

gnuplot strange_multi.plt -persist

On some invocations the frequency bars appear in the first sub-plot, 
on other invocations they do not appear, the upper plot shows no 
data. But if I write the plot to file using, say, pngcairo or 
pdfcairo, the first sub-plot is always OK.

Am I misusing multiplot or might there be a bug here?

-- 
Allin Cottrell
Department of Economics
Wake Forest University