[firefoxxy]

Okay, that's embarrassing... You were right: When I just looked into my personal.ini it wasn't there. So I copied replace_br_with_p: true into my personal.ini. I closed it, opened it again because I was not sure if I might have closed the settings by escape instead of clicking ok. And it was there. Then I deleted and re-downloaded the fic. I opened the ebook, again it had the odd spacing. I went back to my personal.ini - and the replace_br_with_p: true line was gone.

I closed and restarted calibre. Added the setting once more, restarted, and re-downloaded the story again. It worked. Thank you.

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I don't want to spam the forum, so I'll add this here, too. Sorry for being such a bother.

The replace_metadata is not working well for this story and I can't figure out what the problem is.

While it does change Canon Snape and Injured Snape correctly it doesn't work with Depressed Snape, Colleague Snape and Harry, Snape Equal status to Harry.

I tried using category instead of genre, but that didn't help either. The rest is the same as in the personal.ini above.

Spoiler:

replace_metadata:
 takesplaces=>^0 - Pre Hogwarts.*$=>0 - Pre Hogwarts&&category=>Kid Fic
 snapeflavours=>^Angry Snape$=>Angry Severus&&category=>Anger
 snapeflavours=>^Comforting Snape$=>Comforting Severus&&category=>Hurt-Comfort
 snapeflavours=>^Depressed Snape$=>Depressed Severus&&category=>Drama
 snapeflavours=>^Desperate Snape$=>Desperate Severus&&category=>Drama
 snapeflavours=>^Kind Snape$=>Kind Severus&&category=>Fluff
 snapeflavours=>^Loving Snape$=>Loving Severus&&category=>Fluff
 snapeflavours=>^Overly-protective Snape$=>Overly-protective Severus&&category=>Protectiveness
 category=>Colleague Snape and Harry=>Colleagues&&ships=>Harry & Severus
 category=>^Guardian Snape$=>Guardian/Mentor&&ships=>Harry & Severus
 category=Snape Equal Status to Harry=>Harry Equal Status to Severus

Thank you for having a look.