Hi Eddy F ( and Yasuaki Honda):
I find (on Windows...) that the default settings for plotting allows
only one plot at a time.
To resume Maxima, you must kill the (gnuplot) window by clicking on the
[X]. Maybe the
same kind of thing is happening on Android -- you have a plot process
that is taking
precedence over the Maxima main window and taking all input.
I think there are other settings that allow multiple plots(on windows),
so maybe your default setting is
not right.
RJF