Last modified: 2012-07-23 17:59:04 UTC
/64 is a rather paltry limit for IPv6 rangeblocks, due to the way addresses are allocated. Any true rangeblock will have to span multiple /64s, especially since users also may get /60s, /56s, or even /48s.
See https://gerrit.wikimedia.org/r/10387
Patch was merged, but before that can this change be placed in CommonSettings.php or InitialiseSettings.php?