"Create Paintbrush" won't work correctly

Essentially I want to make a custom brush using the Create Paintbrush option. I select what I want and hit the button to create the brush. Animate will try to create a brush with a completely different object I haven't selected during a session. I've tried closing and reopening the app, as well as unselecting it and retrying. This feature has only worked twice out of how many times I've tried.