This is a bug that was introduced in Binky while trying to fix the other bug that I've mentioned before. The first time you add a number it will work, however the second time it's indexed it won't - that's why I initially wasn't able to reproduce the problem.
I've just fixed this bug in DokuWiki. You can either manually apply the
changes in inc/indexer.php or simply download and replace the changed file
inc/indexer.php in your installation, this is identical to the file in the Binky release just with my fix.
Thank you very much for noticing the problem and sorry for the bug (I'm also the one who introduced it while fixing the other bug).