The way that we have solved it is to add a calculation on a custom form for each issue. Calc = ABS(1), which counts each issue as 1 record.
Then, we created a report where we summed the counts and charted them in columns. Y-axis is the count, X-axis is the issue name. You can then scan the chart quickly to see if there any duplicates. If no duplicates, you will see a chart column with all values of 1. As soon as there is a duplicate, you'll see one spike that is easy to identify. You can then hover over that to see the duplicate value.
It's not the best solution, and unfortunately you can't filter on only the duplicates, but it has worked for us.