Although accepting a gryphon ride from Gryphoneer Windbellow automatically switches you to your original form, you still get the error message “can’t use items while shapeshifted” when trying to use the bomb. This seems to happen only when starting out in flight form. (It may also happen with the ground version of travel form but I would have to start a new druid to test this.) I then tried cat, bear, and moonkin forms, and they all allow use of the bomb. The issue persists even with all add-ons disabled.