Is the sentence
I didn't hear what you've (just) said
a natural one? Some tell me that it's unnatural, but not ungrammatical. Others tell me that it's all right. I'm puzzled. What do you think? The trouble seems to be the usage of present perfect ("you've said") after past simple ("didn't hear").
Let me add a subquestion. Would you be likely to use the above-quoted sentence at all? I don't care much if it's grammatical or not, I would like to know if any native speaker speaks like that nowadays.