whk@machine:~/.../bin/Debug$ mono tasks.exe

(tasks:23360): Gtk-WARNING **: Invalid text buffer iterator: either the iterator is uninitialized, or the characters/pixbufs/widgets in the buffer have been modified since the iterator was created.
You must use marks, character numbers, or line numbers to preserve a position across buffer modifications.
You can apply tags and insert marks without invalidating your iterators,
but any mutation that affects 'indexable' buffer contents (contents that can be referred to by character offset)
will invalidate all outstanding iterators
Stacktrace:

  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) Gtk.Application.gtk_main () <0xffffffff>
  at Gtk.Application.Run () <0x0000b>
  at tasks.MainClass.Main (string[]) <0x0003f>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <0xffffffff>

Native stacktrace:

   mono() [0x4b1fac]
   mono() [0x5085de]
   mono() [0x428f2d]
   /lib/x86_64-linux-gnu/libpthread.so.0(+0xfc90) [0x7f7675a86c90]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1d3beb) [0x7f767210abeb]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1d410e) [0x7f767210b10e]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(gtk_text_layout_get_line_display+0x11a) [0x7f7672113a7a]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1ddc42) [0x7f7672114c42]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1c2005) [0x7f76720f9005]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(gtk_text_layout_validate_yrange+0x21a) [0x7f7672112faa]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1ea91d) [0x7f767212191d]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1eca5d) [0x7f7672123a5d]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(+0x1eca99) [0x7f7672123a99]
   /usr/lib/x86_64-linux-gnu/libgdk-x11-2.0.so.0(+0x1dd87) [0x7f7671c9fd87]
   /lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_dispatch+0x15d) [0x7f766bd3ab6d]
   /lib/x86_64-linux-gnu/libglib-2.0.so.0(+0x49f48) [0x7f766bd3af48]
   /lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_loop_run+0xc2) [0x7f766bd3b272]
   /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0(gtk_main+0xb7) [0x7f7672067747]
   [0x40a219da]

Debug info from gdb:

Could not attach to process.  If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/llama/ptrace_scope, or try
again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operación no permitida.
No threads.

=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================

Abortado (`core' generado)