Oh, this is from the cange to real YAML syntax. When you really want tag: * post as search query, than write it the following way: search "tag: * post", but i think the search is invalid with tag:` becaus the tag has no parameter.
I will include this in the documentation as a hint.
EDIT1:
Error: Nested mappings are not allowed in compact mappings
This error message occurs when a colon is used in the option value and an space character follows the colon. Just enclose the value of the option in quotes like alias: "title AS : Title :".