this may overlap some of the other issues reported here but didn't quite seem to fit any of them.
i have a form that has an imagefield and a flexifield. if the flexifield is set to use only one content type, everything is fine. but if it is set to allow more than one content type, then changing the type widget from "Please select" to one of the types will not open up a form - IF i have not yet uploaded an image to the imagefield. once i've done that upload then the flexifield works fine.
in Safari, trying to pick a content type in the flexifield produces an error, "TypeError: Result of expression '(jQuery(this).data('form-plugin-onload'))' [undefined] is not a function." that doesn't come from any particular file so i assumed it's a minified js file somewhere.
if the flexifield is set to an Unlimited number, and i add another item, it makes the forms for the existing flexifields appear.
i have no idea how to begin debugging this.
i didn't report it as a bug because i set up a vanilla Drupal installation with nothing but flexifield and imagefield and their required modules and could not recreate the problem. so there is some other source of trouble in my particular setup. i'm hoping someone may have some ideas about how to try to track that down.
this is with the latest dev versions of all the involved modules, btw.