Thanks for reporting and supplying a patch @malcomio
The patch in #2 is incom...

Thanks for reporting and supplying a patch @malcomio

The patch in #2 is incomplete.

The base svg sprite in base theme `base_theme/images/icons.svg ` gets replaced by the active sub theme svg sprite at `sub_theme/images/icons.svg` in line #21

I am attaching a new patch herein in which the icon span will be appended instead of replacing the icon sprite content on the page.

The patch literally consists on of one dot :D One of the reasons why I love PHP :)