American Opportunity Credit bug?

 

So my son was in his 4th year of college 1/2019 but had not completed it yet.  My AGI is not over 180K married filing jointly and we have only claimed the American Opportunity Credit for 2 years so far.

 

Therefore, I should be able to claim it, right?  He is claimed as a dependent.  He is 23.  If I choose that he goes to school "full time" it won't let me claim it.  If I change it to "half time" it does let me claim it.

 

Am I missing something or is this a bug in turbo tax?