vim interface broken, new line on every keypress

When using vi/vim, a new line is created on every keypress instead of overriding the current one(s).
So writing "Hi" looks like this:
```bash
~
H
~
Hi
~
```
The 'static interface' at the bottom (mode, filename, cursor position etc.) is duplicated as well every time, which pushes everything else up and out of the window - so before you scroll, you don't even see what you've written. Here is a GIF showing the issue:


Editing using nano works without problems and vim in Hyper also works flawlessly.

I'm using WSL (Ubuntu) on Windows 1809