We're trying to implement some agile/lean practices in our software development, and one thing I've read is not to maintain a long "wish list", but to keep the product backlog as short as possible with detailed notes only about the things near the top of the list. I can clearly understand the reasoning behind this.
However, often we will have a case where a customer of a tester finds an obscure problem or edge case. We usually do some investigation to find the exact source of the problem so we know how serious it might be (e.g. could it affect other cases?) and often consider how we would solve it and/or what workarounds are available. In some cases we don't go through with the actual fix because we think the cost/benefit isn't worth it at the time, but I still want to record the results of our investigations so that if the problem happens again in future, it's easy to recognize it and see what workarounds we used, and because we might decide that it's worth fixing it after all
At the moment we create a jira ticket with a special category called "wish list" for anything like this. Is there are more "agile" approach we should be using?
Be ruthless with your jira's, there is nothing to be gained by documenting every issue you find. Remember the agile manifesto - "Working software over documentation".
Fix the blockers right away, put the critical ones in the backlog and schedule in the next sprint, for anything that isn't worth fixing, do the investigation (always investigate bugs), write a few quick notes, and close it with the jira status 'wont fix'.