Gtkmm program with strange crashes

[Jonas Platte <jonasplatte myopera com>]

Hello,
I'm having some weird problem with my Gtkmm program. I updated it to 
only load one dialog with Gtk::Builder if that dialog is needed. I only 
changed the time it is loaded and moved it into it's own .ui-file and 
now my program crashes on usage of this dialog, but _only sometimes and 
not at construction of the dialog_. What is really strange is that the 
program crashes in a part of the code I didn't modify and that should 
not be influenced by Gtk::Builder:

ref_year_ListStore->clear();

ref_year_ListStore is a RefPtr to a ListStore for a combobox with only 
one column (ustring) and is initalized in the constructor of my class. 
It is not modified anywhere else, it is only dereferenced and passed to 
Combobox::set_model. Here is the initialization:

ref_year_ListStore = Gtk::ListStore::create(combobox_year_column);

I have two types of crashes, one where it crashes when dereferencing the 
RefPtr, and one where it crashes in clear().
I've added the stack traces as attachments. Has anyone got an idea where 
this crash could come from?

Attachment: Stack Trace 1
Description: Text document

Attachment: Stack Trace 2
Description: Text document