PRS+ custom formatting is inconsistent

I just installed PRS+ on my reader. I loaded the fonts and I loaded a custom CSS file as follows:

@font-face {
font-family: "Charis";
font-weight: normal;
font-style: normal;
src: url(res:///Data/fonts/CharisSILR.ttf);
}
@font-face {
font-family: "Charis";
font-weight: bold;
font-style: normal;
src: url(res:///Data/fonts/CharisSILB.ttf);
}
@font-face {
font-family: "Charis";
font-weight: normal;
font-style: italic;
src: url(res:///Data/fonts/CharisSILI.ttf);
}
@font-face {
font-family: "Charis";
font-weight: bold;
font-style: italic;
src: url(res:///Data/fonts/CharisSILBI.ttf);
}
body {
font-family: "Charis";
text-align:justify;
font-size: medium;
line-height: 3.2em;
margin-top: 1em;
margin-left: 1em;
margin-right: 1em;
}

(I used that huge line height to test if the line height was being respected or not.)

When I open books, some of them are using the Charis font, and some are not. The books that are not using the Charis font are not using a custom font, they are using the default Sony font. Some of these books are using the default Sony font, but they have the margins and line-height that I set. Some books *are* using the Charis font, but the margins and line-height are not being respected. One book had a huge margin when I loaded it, and it still has a huge margin now.

What's going on here?

eP