Created attachment 152469 [details]
Reproduce problem

Create interface type using g_type_register_dynamic and then try to implement this interface in some type (using g_type_add_interface_static or g_type_add_interface_dynamic). Segfault.

Attached test reproduce this problem. For simplification, this test use GTypeModule type registration, but same occures when implementing GTypePlugin in some class and use object of this class in g_type_register_dynamic(). 

Moreover, plugin object isn't used at all(via use_plugin) when implementing dynamically declared interface, even prior g_type_default_interface_ref() on interface type doesn't help.

Problem appears in 2.23 version of library, previouse versions process implementation of dynamically declared interface correctly.