Perhaps only a certain subset of users have the problem, or it only occurs in certain situations. Say as much as you need to allow others to confirm or challenge your assumptions. The more open you are about the sources, the less likely people will be to suspect them. If you work on a team, create a short document that lists all of the problems, and include the supporting information with each one. It is difficult to navigate from one section of the Web site to another.
Users have to wait too long for the software to load.
Our security error messages are difficult to understand. The registration page has too many questions, and users often abandon it. Finding a specific product on the site index is too hard to complete. I draw the line based on two characteristics. The act of taking a list of items, and ranking them by priority, defines a release.