Found in the Post-Gazette:
Is it possible that Pirates have underestimated his potential?
Jim Maruca of Ross Township
KOVACEVIC: No, probably not, Jim. The Pirates had many internal discussions related to Castillo this offseason, even in the week leading up to his release, and there certainly was a faction of management that was leery of letting him go because they worried that he could become "an All-Star somewhere else," as one of them described it. It was not a decision reached easily, from what I gather.
At the same time, it is common in sports where an athlete needs a change of scenery to blossom. His view of the team's belief in him, his sense of a fresh start and his urgency to make the most of a second chance can lead to greater confidence and greater performance. Whereas, if he stays put, he stagnates.
The Pirates did try to trade Castillo and they probably would have taken just about anything for him, but the other teams correctly guessed that the Pirates soon would non-tender him, anyway. So, the Pirates let him go.
Is this one that comes back to bite them? Within the above scenario, I would say no such thing is possible, at least not as far as blaming current management is concerned. But - and this is important - there remains no firm explanation for how previous management handled Castillo, particularly in 2007. He had options remaining and could have spent time in the minors working out his various issues, but the team chose instead to keep him in the majors, rotting and pouting on the bench.
One of the strangest decisions of the year.
Make of the above what you will, but one thing did strike me: He has options left. In other words, if he makes the club and stinks up the joint the Marlins can just send him down to the minors and bring someone else up. And given the way the Marlins had to shuttle players the last few years between the big club and the minors, it is nice to know that Castillo is a moveable player and isn't necessarily stuck on the 25-man roster.