Declaration of views_content_cache_key_node_only::options_form() should be compatible with that of views_content_cache_key::opti

Don't know if this is a bug or something I am doing wrong.

I get the following error on setting views caching to Content-based + Node type X:

Strict warning: Declaration of views_content_cache_key_node_only::options_form() should be compatible with that of views_content_cache_key::options_form() in _registry_check_code() (line 3066 of XXXX/includes/bootstrap.inc).

This is a nested view. Both, the amster view and the sub-view are on the same setting. I've attached the view code in a txt file.

Does anybody know what's going on?

Thanks for all the hard work, btw!