mate-panel crashed with signal 7 in g_hash_table_foreach()

[Winfried Pohl]

some applications freeze (firefox, openshot,..). After restarting the X-server, the applications freeze mostly again. So I have to reboot.

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: mate-panel 1.12.2-1
ProcVersionSignature: Ubuntu 4.4.0-7.22-generic 4.4.2
Uname: Linux 4.4.0-7-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CrashCounter: 1
CurrentDesktop: MATE
Date: Wed Feb 24 13:40:28 2016
ExecutablePath: /usr/bin/mate-panel
InstallationDate: Installed on 2016-01-16 (38 days ago)
InstallationMedia: Ubuntu-MATE 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160103)
ProcCmdline: mate-panel
ProcEnviron:
 LANGUAGE=de_DE
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
Signal: 7
SourcePackage: mate-panel
StacktraceTop:
 ?? () from /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0
 g_hash_table_foreach () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
 gtk_rc_reset_styles () from /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0
 g_closure_invoke () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
 ?? () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
Title: mate-panel crashed with signal 7 in g_hash_table_foreach()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
XsessionErrors:
 mate-session[2497]: WARNING: Unable to find provider '' of required component 'dock'
 (mate-panel:2613): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
 (blueman-applet:2679): Gdk-CRITICAL **: gdk_window_thaw_toplevel_updates: assertion 'window->update_and_descendants_freeze_count > 0' failed
 (nm-applet:2701): Gdk-CRITICAL **: gdk_window_thaw_toplevel_updates: assertion 'window->update_and_descendants_freeze_count > 0' failed

[Apport retracing service (apport)]

StacktraceTop:
 gtk_rc_clear_realized_style (key=0x888810, value=<optimized out>, data=<optimized out>) at /build/gtk+2.0-tESQz7/gtk+2.0-2.24.29/gtk/gtkrc.c:1665
 ?? ()
 ?? ()
 ?? ()
 ?? ()