Application doesn't leak memory running valgrind

Hello list,

I have a Qml application that leaks memory when run normally.  I've
reduced it to a very simple Qml app and it still leaks.  And the leak
is visible with pmap almost immediately.  The application runs on an
embedded device (armhf).

When I run it with valgrind:

 /usr/bin/valgrind.bin --tool=memcheck --error-limit=no \
--log-file=vg-220214.log  --leak-check=full \
--leak-resolution=high --show-reachable=yes ./qml-mwe3

There is no leak.  I've tried running it for a solid day and pmap
doesn't show any leak.

If I run the same application in gdb (just letting it run).  It leaks.
 However, if I put a break point on malloc:

gdb ./qml-mwe3
(gbd) run
--- some time passes ---
^C
(gdb) break malloc
(gdb) commands
> continue
> end
(gdb) run

Then the leak stops.  No memory is freed, but it absolutely stops
increasing.

Can anyone offer any guesses as to what's going on?  I would appreciate
any ideas to debug this further.

Thanks,
Stef