If I recall he struggled for a stretch mid season. I think a terrible month of June losing his 8th inning role.
Yup. Actually, June 6-18, 2013, Burton pitched 5 games and allowed 8 runs, same as 2014 so far. Actually, June 6 thru July 1 last year, he had 10 games, 12 runs. Followed it up with a stretch of 19 games, 6 hits, zero runs. (We won't discuss how he pitched after that -- suffice to say, he closed out the season in classic 2011-2013 Twins fashion.
As to the extension, Burton's $3.25 mil isn't hurting the team in the least bit. Heck, his roster spot isn't even under that much pressure -- Tonkin is it, really, and they've already got him on the roster thanks to another guy on the DL.
If his poor pitching continues over the next few weeks, we can think about cutting him loose. Otherwise, try to get him back to general 2012-2013 levels, and if he gets on a roll again, maybe someone will want a flyer on him for August/September (or 2015 with his $3.6 mil team option). Not that he will bring back much in trade, or provide us with a whole lot performance-wise in the intervening months, but it wouldn't take much to justify his modest salary.