There is a bug in Clang 3.4.2 that causes wrong data tree traversal, which results in a crash. It can occur during any traversal but it was observed in XML printer while printing default values. The solution is to compile using either GCC or newer version of Clang. Starting from which version it works we do not exactly know. Clang 5.0.0 works fine.
libyang uses its own XPath implementation to evaluate XPath expressions. The implementation completely lacks support for axes. Nevertheless, it should always be possible to write equivalent expressions without the use of axes.
If there are any XPath expressions defined as part of a deviation, they include literals, which are directly compared with identityref nodes (testing whether an identityref has a specific identity value), and the identity literal used is from the deviation module (meaning it could be written without a prefix), the prefix is mandatory for libyang to evaluate the XPath expression correctly.
NMDA RFC specifically defines that the parent data node of an invoked nested notification or action must exist in the operational datastore. This validation is not implicitly performed by libyang when validating the operation so if the validation is supposed to happen in full compliance to this RFC, parent existence must be checked explicitly.
Since libyang 1.0, there is a check to make sure that the (user type or extension) plugin was compiled with the compatible API version. In case there is a plugin with incompatible API version, the following warning is generated by libyang:
libyang[1]: Processing "user_date_and_time" user type plugin failed, wrong API version - 1 expected, 0 found.
The default path for the plugins is /usr/local/lib64/libyang/ so you can clean it up manually or set a different plugin directory via LIBYANG_EXTENSIONS_PLUGINS_DIR or LIBYANG_USER_TYPES_PLUGINS_DIR environment variables.