Hi,
I am not sure if I am missing a theme setting for this, or if it is a bug in the highlighting, but it appears that selections remove font styles like italics. I have comments set to be italic in my theme with
<dict>
<key>name</key>
<string>Comment</string>
<key>scope</key>
<string>comment</string>
<key>settings</key>
<dict>
<key>fontStyle</key>
<string>italic</string>
<key>foreground</key>
<string>#586E75</string>
</dict>
</dict>
But when selecting text that contains a comment, the comment is rendered normal inside the selection highlight.