They mean nothing. It is most likely a minor bug fix, which the developer did not deem large enough for a new number, so he just added a letter instead.
It could just as fine be v6.30.1 or something.
For the record 1.0 is normally the first non-beta version.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.