proj: in headers does not apply to newly created tasks

[djugei]

=== Test | proj:test ===
*[ ] testtask

and

=== Test | proj:test | proj:test ===
*[ ] testtask

both create the task, but do not assign the proj: tag to it. it therefore disappears from the list. Filtering still works though.

using latest git. this used to work on the (very old) release.