long rightwards double arrow ⟹ should be longer and rightwards double arrow ⇒ should be shorter

Package: emacs
Version: 1:26.1+1-3.2ubuntu2

How to reproduce:

1) Run emacs-gtk

2) Enter the text in the title ("long rightwards double arrow ⟹ should be longer and rightwards double arrow ⇒ should be shorter") into the scratch buffer

3) Observe that ⟹ (U+21D2) is shown short and ⇒ (U+27F9) is shown long in the emacs buffer (cf. the attachment). But it should be the other way round!

M-x describe-font [Enter][Enter] returns the following:

name (opened by): -DAMA-Ubuntu Mono-normal-normal-normal-*-13-*-*-*-m-0-iso10646-1
       full name: Ubuntu Mono:pixelsize=13:foundry=DAMA:weight=normal:slant=normal:width=normal:spacing=100:scalable=true
       file name: /usr/share/fonts/truetype/ubuntu/UbuntuMono-R.ttf
            size: 13
          height: 14
 baseline-offset: 0
relative-compose: 0
  default-ascent: 0
          ascent: 11
         descent: 3
   average-width: 7
     space-width: 7
       max-width: 7

I see the symbol width as expected in the character table for the font Ubuntu Mono, therefore, I personally don't say that the font is guilty, though the reader may do it if they think otherwise.

$ lsb_release -rd
Description: Ubuntu 19.04
Release: 19.04