Because it was added to my custom CSS as last lines by Scrivener it affected the text-indent of any .xhtml file because they are all build this way (as I described earlier) and had all the div wrapper with class “heading”.
That means that any HTML element that hadn’t a specific overrule for text-indent was affected (as along as it has the CSS property “text-indent” of course).
Because I couldn’t find the origin of this rule I had to unnecessarily overrule the indentation of a couple of other elements who showed up that unwanted indentation behavior.