Font/Letter Size doesn't change

Hey guys,

I experienced an unexpected problem. After adding a new epub file, i wasn't able to change the font size...

The text is styled with this:
.style0{ font-family:TimesNewRoman;font-style:;font-weight:; font-size:10.729065px; }

That should be enough to be readable.

In my Kobo Aura text settings, I can change the font-family, the font-size, the line spacing and the border.

But if I de/increase the font-size, the line spacing de/increases!
If I de/increase the line spacing, the line spacing de/increases normally.

Has anyone of you experienced this?