Here’s an example of (probably) overgeneration in the Spanish Grammar (note the agreement error between person and famous):
(1) *Mis abuelos son personas famosos. My grandparents be.3PL.PRES.IND person.PL.FEM famous.PL.MASC Intended: My grandparents are famous people [spa]; sounds really, really bad.
The reason the structure exists is illustrated in example (2) below:
(2) Ellas hacen musica juntas They.PL.FEM do.3PL.PRES.IND music together.FEM.PL `They play music together.' [spa]
Sentence (2) has a very similar structure—which is correct for it, probably.
(3) ?Mis abuelos son personas juntos "My grandparents together are people".
is possible to say (though awkward).
(3) *Mis abuelos hacen musica famosos Intended "My famous grandparents play music".
doesn’t seem to be possible.
Of course adjectives can mostly be predicative adjectives (the intended sentence (1)). So, famoso should be able to go through the AP->PP rule (which is called “predicative-phrase” in the grammar).
What shouldn’t happen then is: the resulting PP should not be modifying the VP “play music”?
So the difference is both between junto and famoso and between ser and hacer? Both between the two adjectives and the two verbs?
Are there existing analyses in other languages for this?