Translation:Isn't it short?
I have this same question. In English "Isn't it short?" feels more like a statement of one's own opinion and asking for confirmation; it could even be very judgemental depending on the context. "It's not short, is it?" feels much more concerned/more iterested in the other person's opinion. Which would be the more accurate sentiment in Japanese?
"Isn't it short?" means that you think that it's short and you're asking if you are wrong
"It's not short, is it?" means that you think that it's not short and you are asking if you are wrong
So in both sentences you are asking for confirmation of what you think, but they express opposite opinions. If it doesn't feel too clear for you, just look at the questions: the first one is asking "isn't it short?" and the second one is asking "is it short?", so they are asking the opposite thing
Well; if you take "it's short, isn't it?" to have the same meaning that "isn't it short?", then yea. Although "it's short, isn't it?" seems to indicate a stronger opinion on the speaker, which I guess would correspond better to the sentence 「みじかいですね（？）」, where the ね would stand for "isn't it?" (="right?", which is the function that ね usually does)
The speaker is saying - isn't it short?!!!?
Meaning - wow, that's really really short!!! Don't you agree that it's really really short?
Also, the speaker is expecting the answer to their question to be positive ie. They are expecting the listener/s to respond something like - wow, you're right! That IS really really short!