Bug Tracking System with threads

I'm looking for a bug tracking / feature tracking system that is designed with categorized threads.

For instance, we are using one with set fields for submitting the problem, describing the solution, test steps, test results, and then when it goes back with some more problems, all the fields are already filled in from previously and you can't differentiate between the original stuff in the fields and the new comments you want to make. What a nuisance! (axosoft)

So I want something that allows submission as threads.
You submit a comment, categorize it under the possible categories and all you have to look at are the ones at the bottom to see the new stuff. You can comment and ask questions back and forth without having to have a ton of custom fields on a screen. I just want a threaded, categorized list, that allows pasting of images within the comment boxes (not uploads and attachments, but true pasting in, unlike Experts-Exchange which requires an upload and embedding).

Anyone know of such a thing?

thanks!