It appears that special properties defined as one of the types pointing to a special namespace don't work. "Has default form" is one such property - it's defined as being of type "__spf", and it can't be successfully queried on in the latest version of SMW, 1.5h. This means that "edit with form" tabs no longer show up, which is very bad; it also leads to other strangenesses like this:

http://discoursedb.org/wiki/Property:Has_default_form

Version: unspecified
Severity: critical