Repair also fails in this way...
On PAR2-tab, some files can be displayed as being without problems, but when Repair is running, is fails, due to misspelled filenames (since ABZ is adding x to the end of the extension, ie. r28x instead of r28).
Using QuickPar instead, it finds the two .r28's, will automatically use the correct one (without errors), and notices that the file has a wrong name.
(build 0.24.6)