For those of you who can read Catalan:
On the blog Quaderns de Lavínia, Rosa Delor has written an article on self-translation in the case of Jordi Vintró's bilingual poetry collection Insuficiència mitral (Editorial Lumen, Barcelona, 1997, bilingual edition). Unfortunately I don't understand much of it, but what I found striking was that Jordi Vintró commented on the blog entry!
As far as I know this is the only time Vintró self-translated.
You can read a fragment of Insuficiència mitral in Catalan and Spanish here.