I believe it is possible to disprefer something while either 1. not disliking it, or 2. liking it but not intensely enough to be the preference. As in, "I like tart apples, but I sometimes disprefer them as an ingredient on a green salad." It doesn't and hasn't, meant I would refuse to eat a salad with this ingredient included, but there are times when my preference would have been to have a salad without them.

I think you linguists worry too much. It's a simple enough formation using a very common prefix, and while it is not clear whether "I disprefer" means "I do not prefer" or "I prefer something other than" or "I prefer the opposite of" or "I stop preferring", either it'll settle down to one meaning or it'll carry a range. So what? This is the first time I've heard the word but I don't find it particularly puzzling.