Why? Just why?
(I suppose you could paraphrase this as "Why isn't the '=' block case sensitive?")
this should be in snap! bugs not help with snap!
Done.
I'm not sure about the technical reason, but that's just how it's always been (in Snap!).
If you want case-sensitive comparison, use 
.
It can be inconvenient at times but I think if you have case sensitivity, you might find a lot of bugs popping up that would be hard to find. At least, that's why I think it's like that.
As said, you can use the "is identical to" block to have case sensitivity.
I don't think this is a bug.