Ah, this seems to be a bug in the Debian valgrind wrapper, adding the --suppressions command multiple times when valgrind reexecutes itself. I fixed that, but now it seems to me that valgrind is stuck in an infinite loop of reexecuting itself:

master@piperine:~$ strace -p28547 2>&1|grep ^exec
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0
execve("/usr/bin/valgrind", ["valgrind", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/bin/valgrind.bin", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 42 vars */]) = 0
execve("/usr/lib/valgrind/amd64-linux/memcheck", ["/usr/bin/valgrind.bin", "-v", "--leak-check=full", "--leak-resolution=high", "--num-callers=50", "--log-file=/tmp/xfdesktop-valgri"..., "/usr/lib/xfce4/panel-plugins/xfc"..., "socket_id=16777267", "name=xfce4-menu", "id=12098086641", "display_name=Xfce Menu", "size=36", "screen_position=11"], [/* 43 vars */]) = 0