Hi,
I've just had a play with it and I see the same problem. I looked up the log entry for it and saw:
2016-05-13 14:17:35 <ip> <username> <host> np_cat=op&title=XXXtest&do=edit&id= Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Firefox/38.0
I then scanned the directory tree as follows:
find * -type f -exec grep np_cat {} \;
But only saw the three entries ( 2 in syntax.php and on in the javascript) that are in addnewpage. Nothing else, not even a "binary matches" message.
Searching the fora for np_cat, all I could find was
https://forum.dokuwiki.org/thread/5546 which is a Chinese language entry from 2010 which was aparrently fixed in 2013. Following the link from the 2013 message leads to a 404 error.
Searching the Wiki yielded nothing.