In my 15.2 test system - when I open nm-panel to see what ip my system got - it show it but when you exit it looks like MATE dies and comes back with all the windows moved about. It does it every time I try it. This show up in the journalctl:
May 18 23:24:49 VM13 kernel: show_signal: 5 callbacks suppressed
May 18 23:24:49 VM13 kernel: traps: marco[1727] general protection fault ip:7f7c645a60e0 sp:7ffc17ab7588 error:0 in libcairo.so.2.11600.0[7f7c6453f000+130000]
May 18 23:24:49 VM13 systemd[1]: Created slice system-systemd\x2dcoredump.slice.
May 18 23:24:49 VM13 systemd[1]: Started Process Core Dump (PID 4041/UID 0).
May 18 23:24:49 VM13 systemd-coredump[4042]: Process 1727 (marco) of user 1000 dumped core.
Stack trace of thread 1727:
#0 0x00007f7c645a60e0 cairo_region_num_rectangles (libcairo.so.2)
#1 0x00007f7c666082fe n/a (libmarco-private.so.2)
#2 0x00007f7c6660ae95 n/a (libmarco-private.so.2)
#3 0x00007f7c66306dd7 n/a (libglib-2.0.so.0)
#4 0x00007f7c6630a3b4 g_main_context_dispatch (libglib-2.0.so.0)
#5 0x00007f7c6630a750 n/a (libglib-2.0.so.0)
#6 0x00007f7c6630aa12 g_main_loop_run (libglib-2.0.so.0)
#7 0x0000559710076a6a main (marco)
#8 0x00007f7c65f2134a __libc_start_main (libc.so.6)
#9 0x0000559710076e5a n/a (marco)
Stack trace of thread 1728:
#0 0x00007f7c65fee6db __poll (libc.so.6)
#1 0x00007f7c6630a6c9 n/a (libglib-2.0.so.0)
#2 0x00007f7c6630a7dc g_main_context_iteration (libglib-2.0.so.0)
#3 0x00007f7c6630a821 n/a (libglib-2.0.so.0)
#4 0x00007f7c66333cde n/a (libglib-2.0.so.0)
#5 0x00007f7c6194a4f9 start_thread (libpthread.so.0)
#6 0x00007f7c65ff8f2f __clone (libc.so.6)
Stack trace of thread 1732:
#0 0x00007f7c65fee6db __poll (libc.so.6)
#1 0x00007f7c6630a6c9 n/a (libglib-2.0.so.0)
#2 0x00007f7c6630a7dc g_main_context_iteration (libglib-2.0.so.0)
#3 0x00007f7c58ce35bd n/a (libdconfsettings.so)
#4 0x00007f7c66333cde n/a (libglib-2.0.so.0)
#5 0x00007f7c6194a4f9 start_thread (libpthread.so.0)
#6 0x00007f7c65ff8f2f __clone (libc.so.6)
Stack trace of thread 1729:
#0 0x00007f7c65fee6db __poll (libc.so.6)
#1 0x00007f7c6630a6c9 n/a (libglib-2.0.so.0)
#2 0x00007f7c6630aa12 g_main_loop_run (libglib-2.0.so.0)
#3 0x00007f7c6405f4c6 n/a (libgio-2.0.so.0)
#4 0x00007f7c66333cde n/a (libglib-2.0.so.0)
#5 0x00007f7c6194a4f9 start_thread (libpthread.so.0)
#6 0x00007f7c65ff8f2f __clone (libc.so.6)