a program halts on background and doesn't get the focus back

Hi all,

I've been using Ratpoison + Screen + keynav on Debian (now on its
Raspberry Pi's variant Raspbian) for many years.

Now I have a strange problem for the first time.

I use SMSQmulator (http://www.wlenerz.com/SMSQmulator/), an emulator,
written in Java, of the SMSQ/E operating system.  The problem has two
parts:

1) This program halts when its window is not visible, and it continues
when I select its window in order to make it visible.  It works fine
when its window is on its own frame, thus visible.  First I thought it
has something to do with the refreshing of the emulated display, but
after some tries it was clear the emulator always halts, no matter if it
needs to update its display or not.

2) This program does not get the keyboard focus back when I select its
window (or its visible frame, no difference). I have to clic on it with
the mouse (with keynav in my case).

First I thought these problems have something to do with the emulator,
and I was about to contact its author, but then I decided to install and
try other window managers, just in case...  Surprise!: no problem with
Openbox, dwm or i3. The emulator works normally when its screen is not
visible, and it gets the keyboard focus back when its window is
selected.

Then I replaced Ratpoison 1.4.5 (the version included in the current
Raspbian) with latest 1.4.8, which I compiled, but nothing changed.

Last I tried also the spectrwm window manager... and it doesn't work
fine: same problems, even worse: sometimes the focus can not be
restored. But it seems spectrwm is still less mature than the other
window managers I tried.

What do you think?  Any clue? Is there anything I can do to investigate
this further?

-- 
Marcos Cruz
http://programandala.net