Edit from the 30th of October 2014: The “Balkan SNP” has now been named by FGC: FGC22049.
I was puzzled why the “Balkan” sub-group has 0 at DYS481. Here is a possible explanation: They have a mutation within or close to this Y-STR.
One of them did the BigY. From his results through YFull, and looking at the position of DYS481 (from 8426347 to 8426474 – thanks YBrowse!), I found that he has a mutation at 8426455 from G to A.
My guess is that it was enough to confuse the algorithm that was supposed to find the number of repeats for DYS481.
This is now confirmed. He has asked FTDNA to “manually” recount and they changed his 0 to 25.
edited the 30th of August: FTDNA has been asked to “recount” all our Balkan member: verdict, they all turn out to be 25!