I'm very new to Bourbon, so I might be saying something incredibly stupid and I apologize in advance, but I found no reference about this anywhere.
Shouldn't useless prefixes be avoided? For example, I see that "transition" has "-ms-transition" as one of its outputs, but the "-ms-" prefix was never needed (IE9 doesn't support transitions at all while IE10 supports the prefix-less, standard declaration).
Transition is just an example, I think there are more. The needed prefixes should be the ones found on http://css3please.com.
@Laz75 You are correct. I think the transition mixin has the ms prefix becuase it was introduced before IE10 was released, so in preparation we prefixed it for MS. I'm big into deprecating anything that is out of date or unneeded. Clearly the MS prefix for the transition mixin should be removed.
I took a look through all the current mixins and removed the prefixes which were not longer necessary. Have a look at the changelog for more details: https://github.com/thoughtbot/bourbon/wiki