Using Notepad++ i noticed some syntax higlighting issues when using background colors.

1- Code blocks(comment block) are highlighted including empty areas. I think there should be a distinction between an empty region and a space-containing region. It would provide better sense of line boundaries.
1- Multiline string blocks are highlighted correctly regarding empty/non-empty regions but new line characters look like spaces at line ends. New line characters must not be highlighted.
Your application appears to have turned the 'EOLFilled' style setting on for the comment. This setting may be either on or off.
The selection background appearing when line end characters are selected is necessary to show that the line end characters have been selected.
Those are not selections. They are background colors set in highlighter settings.
I couldn't find EOLFilled setting but i assume it allows to click and enter characters beyond the line end. This is not the case for my editor. I can say EOLFilled is off.
http://www.scintilla.org/ScintillaDoc.html#SCI_STYLESETEOLFILLED
Thanks for the link.
So the only issue is the highlighting of line endings.
When a background colour is defined for a style then that background is used for the range of that style, including any line end characters. I see this as useful and not a bug. There could be an option to use the default background for line end characters if anyone wants to implement it.