As for an ad management plugin, I'm using WordPress' default media uploader. And WP Media Uploader automatically resizes images. But as the ad image is already resized (i.e.: 225 x 100px) it need not to resize into a new file for thumbnail (100 x 100px); because, that thumbnail is unnecessary for the site.

The cause I presented here, may be a very minute for such a solution, but in case, there is any other massive issue that, in such plugin we can stop the auto resizing with WP Media Uploader only on that plugin-uploads - I think that can be a good solution for any site.

Is there a way to use WP Media Uploader, but can stop auto resizing images only onto that particular case uploads?

But I also know that, plugin like Regenerate Thumbnails can override the rules and can do what I prohibited in my plugins for the site's space-savvy consumption.


Question: Apache won't allow multiple name-based virtual hosts
Answer: First off, can you check the log files for errors when you start up Apache?  It might be complaining, and it will give very useful information if it does..

Secondly, are you making similar changes to the SSL side of things?  MOD_SSL is handled via a different config file, and if you're trying to access these sides of things on port 443, you're not going to get all the different sites working.