Mac triage: can't even understand the bug description, let alone tell if it repros :) over to blink CSS team.

Sorry if my description is not all that simple. I try it in other words:

We have:

<p>AB</p>


The font has a substitution (inside the liga feature of the font):

`sub A' B by emdash;` 

Notation: [OpenType Feature File Specification](https://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html)

The renderer therefore shows:

<p>&mdash;B</p>


Now we apply with CSS a formatting to the first letter. 

Instead of

<p>&mdash;B</p>

the renderer shows:

<p>AB</p>



My URL shows a very reduced example and is taken from a real world example but made with a reduced custom font that shows only this problem.

I reworked the explanations and the example-font: https://signalwerk.github.io/css-opentype-substitution/

Thanks for the detailed report and example.