That Evolution mail caching behaviour is really sketchy. I wonder if it could be used for an exploit in the right scenario. If nothing else, it’s a good way to make an email that looks completely different depending on which client it’s opened in.
Well, for that use the differences in HTML&CSS support and filtering ...
I guess the reason they added this was that they noticed many mails contain same tracking images and decided to cut of tracking data that way.
Either way, the correct full URL is fetched with the full query string. It's just how it's cached that is affected.