If you send Bitcoin amount much less than you have, all rest goes for fee

This isn't a bug, it's the definition of how transaction fees work.

Why is this posted now and interesting?

Likely because it appeared here: https://news.ycombinator.com/item?id=15917430

Broken English? I don't get what this is supposed to mean

Huh? This is referring to a specific api call of a bitcoin library. The developer did not fully understand the API he was calling. This has nothing to do with a specific wallet GUI.