Most/all C++ based IO code had a pattern of doing using RNA_struct_property_is_set to check whether a default path needs to be set. However, it returns false for properties restored from "previous operator settings" (property restoration code sets IDP_FLAG_GHOST flag on them, which "is set" sees and goes "nope, not set"). The fix here is to apply similar logic as 10 years ago in the T32855 fix (rBdb250a4): use RNA_struct_property_is_set_ex instead. Reviewed By: Campbell Barton Differential Revision: https://developer.blender.org/D15904