Yes, you can fix that by editing the theme you use (or create a new one if you use the default theme).
Add the following lines in the comics.css file:

.thumb img
{
    max-width: [[COMIC_W]]px;
    max-height: [[COMIC_H]]px;
}

I'll add it by default in the next release.

I have been able to reproduce the problem with the image you provided, I'll investigate.
It does not seem new though, as I had the same result with version 1.7.6.

Your first error is a different one, I'll need the image file to investigate this one too.
If you want you can send it to me using the "private message" option (just under the search field).

You have to set a regular expression (in the "Scan exclusion pattern" option) that will determine which files and folders will be ignored.
The expression is tested against the whole path of each scanned file and directory.
I usually use this tool to quickly test regexp when I need one.

Done.

Good. :)

Did you try to do a force refresh in your browser (usually shift + "refresh" button), or to clear your cache ?

Oops, I delivered the 1.8.1 a bit to quickly.
Here's 1.8.2.

Fixed. Version 1.8.1 is available.