This is a known problem I've seen a few times. See below for some achievements from Choice Chamber. The string just needs to be escaped before it's put into the GTK field.
(samrewritten:389238): Gtk-WARNING **: 11:44:00.755: Failed to set text '<b><3333333333</b>' from markup due to error parsing markup: Error on line 1 char 25: “3333333333<” is not a valid name
(samrewritten:389238): Gtk-WARNING **: 11:44:00.755: Failed to set text '<b><3333333333</b>' from markup due to error parsing markup: Error on line 1 char 25: “3333333333<” is not a valid name
(samrewritten:389238): Gtk-WARNING **: 11:44:00.758: Failed to set text '<b><33333</b>' from markup due to error parsing markup: Error on line 1 char 20: “33333<” is not a valid name
(samrewritten:389238): Gtk-WARNING **: 11:44:00.758: Failed to set text '<b><33333</b>' from markup due to error parsing markup: Error on line 1 char 20: “33333<” is not a valid name
This is a known problem I've seen a few times. See below for some achievements from Choice Chamber. The string just needs to be escaped before it's put into the GTK field.