While in org, if I stand still, I mount a random flying mount.

While moving, I get a "you cannot mount here" instead of instant mounting "Eve's Ghastly Rider" which is instant during Hallow's End

This is correct, even though the Eve's Ghastly Rider is instant during Hallow's End you can't use it while falling or moving. It's plain just not as good as the old broom was.