I have an entity form for which I am using Field Groups for both the entity form ("Manage Fields") as well as the entity display ("Manage Display"). I fully understand that these are two separate "contexts", if you will, and have created the appropriate field groups under each.
In the entity form itself, the field groups work splendidly -- each form element is grouped exactly as I need it to be. But, when a form submission is displayed, any field groups I've defined for display are completely missing from the output, along with any fields inside them. I have verified that as I take form elements out of the field group, they start appearing again, so it's definitely a field group issue.
I am using the default Bartik theme without any changes applied to it. I see the same behavior with the fieldset, "HTML Element", and "div" styles.
I do have Display Suite installed but this entity does not use any custom DS layouts. I have tried disabling DS but see the same behavior.
I am using the latest 1.x dev code as of 2013-05-16.
I believe this is a bug in FG that it's not compatible with entity forms.