Leaping birds on the tower map turn invisible and are immortal until leap is performed

This has existed since the change to the leaping bird behavior in 0.1

The leaping birds if primed to leap will be immortal until getting to my character where they then turn invisible until the leap is executed. Meaning if I run away the bird sprite is invisible. After the leap is completed the bird monster can be attacked. AI seems to prioritize the leap as the first attack so the bird must be avoided since it can't be killed when starting that animation.