I also fail to re-construct the problem on my installation (Linux Mint) : I can continue browse index-terms until after the 3rd click without problems.
If the problem is with the data we will need (a subset of) your data for further testing. E.g. an ISO2709 export of a larger set of records (to obtain sufficient index-terms to be browsed and make getting the weird characters more likely).
To me it seems likely indeed that strings containing single apostrophes ‘ or similar create problems as the scripts themselves also quote the strings. A possible solution would be to use the replace()-function of the ISIS Formatting Language to remove them before ‘producing’ them in the interface (or in the authority list).