I believe the transaction fee section of the Send window should display fees in BTC per byte (B) not per kilobyte (kB). Most fee calculator websites provide data in Bytes not in kilobytes (eg. https://bitcoinfees.earn.com/). Currently users can change currency units (BTC, mBTC, uBTC) but not data units. Recalculating automatically from kB to B is simple. Manually, it is easy to make a stupid mistake and either pay terribly too much fee or far below the required amount. If developers have their reasons to keep data units in kB please at least allow users to customize that in Settings as it has been done for Bitcoin units.
As of 2017-11-11 I am using Bitcoin Core version v0.15.0.0-g3751912e8e (64-bit) from official PPA for Ubuntu.