I compared the xmlrpc from 1.5 with the one from 1.5.1, and I think I found the culprit. In the 1.5.1 version, the else statement that begins at line 583 seems to be the problem
else {
$post_category[] = 1;
}
I commented that part out and the default category is no longer added when I post with ecto.
I’ve noticed that this is still happening with the release version of 1.5.1 and ecto 2.3.2. Is this a WP thing or is it an issue with ecto interfacing with WP?