Sour Hefeweizen

So we brewed this hefeweizen to be shipped to Korea (neat, eh?). When it got there, the client called and said it had become quite 'sour'. Well thats bad!
We tried the stuff we kept in the fridge... it was fine. But it just so happened one of the owners of the brewery had taken a keg of some of this hefeweizen (which is a cloudy unfiltered wheat beer, btw, and quite tasty) out over the weekend and left the remaining 1/2 keg in the car in 30 C weather for a few days. We tasted it, and it was indeed sour. But not really in a bad way... it was a pleasant sour. Kindof like a mild lambic or berliner-weisse. It left a great aftertaste in your mouth.

So I've since taken the keg of sour hefeweizen home to my keg fridge and serving it. I like it, and so do my friends. Its actually too bad we won't be brewing it again.

Why sour?
Well, we did some thinking... it doesn't really taste like contamination from lactobacillus or other spoilage bacteria, the sourness is too mild. We think that perhaps at warmer temperatures either the yeast strain produces the sourness in response to being so warm, or just the natual oxidation of the compounds in the beer is accelerated to produce a sour flavour faster. Perhaps the ester compounds produced by the yeast (bannana aroma normally) cleave into these sour compounds.
Any other thoughts?
Keep in mind that the beer was unfiltered, and we added dextrose to create natural carbonation. The kegs we kept at the brewery were left at room temp for 10 days then refrigerated. The kegs that were shipped were left at room temperature for 3 days then shipped at god knows what temperature (apparently warm...).

Cchheerrss!