claws-mail maildir++ plugin crash when removing mailbox

Thread 1 "claws-mail" received signal SIGSEGV, Segmentation fault.
0x00007ffff79d5ced in gtk_box_pack (box=0x175d570, child=0x2, expand=0, fill=0, padding=0, pack_type=GTK_PACK_START) at ./gtk/gtkbox.c:740
740	./gtk/gtkbox.c: Datei oder Verzeichnis nicht gefunden.
(gdb) bt full
#0  0x00007ffff79d5ced in gtk_box_pack (box=0x175d570, child=0x2, expand=0, fill=0, padding=0, pack_type=GTK_PACK_START) at ./gtk/gtkbox.c:740
        __inst = 0x2
        __t = Python Exception <class 'gdb.error'> No type named TypeNode.: 

        __r = <optimized out>
        child_info = <optimized out>
        __func__ = "gtk_box_pack"
#1  0x00007ffff79d5eb8 in IA__gtk_box_pack_start (box=<optimized out>, child=<optimized out>, expand=<optimized out>, fill=<optimized out>, padding=<optimized out>) at ./gtk/gtkbox.c:818
#2  0x000000000045feaf in alertpanel_create (title=title@entry=0x7fffee32b56f "Mailbox entfernen", message=message@entry=0x10d10a0 "Really remove the mailbox `cweiske@cweiske.de' ?\n(The messages are NOT deleted from the disk)", button1_label=button1_label@entry=0x7fffeb4fcedd "gtk-cancel", button2_label=button2_label@entry=0x7fffee3382d7 "_Entfernen", button3_label=button3_label@entry=0x0, focus=focus@entry=ALERTFOCUS_FIRST, can_disable=0, custom_widget=0x2, alert_type=0) at alertpanel.c:335
        font_desc = 0x106c040
        image = <optimized out>
        label = <optimized out>
        hbox = <optimized out>
        vbox = 0x175d570
        disable_checkbtn = <optimized out>
        confirm_area = 0xbf60f5429
        button1 = 0x0
        button2 = 0x0
        button3 = 0x7fffffffd1d8
        focusbutton = <optimized out>
        label2 = <optimized out>
        label3 = <optimized out>
        tmp = <optimized out>
        title_full = 0x97db30 "\360\234", <incomplete sequence \333>
#3  0x0000000000460596 in alertpanel_full (title=0x7fffee32b56f "Mailbox entfernen", message=0x10d10a0 "Really remove the mailbox `cweiske@cweiske.de' ?\n(The messages are NOT deleted from the disk)", button1_label=0x7fffeb4fcedd "gtk-cancel", button2_label=0x7fffee3382d7 "_Entfernen", button3_label=0x0, focus=ALERTFOCUS_FIRST, can_disable=0, widget=0x2, alert_type=ALERT_NOTICE) at alertpanel.c:101
#4  0x00007fffeb4fa0a4 in remove_mailbox_cb () at /usr/lib/x86_64-linux-gnu/claws-mail/plugins/maildir.so