We had a client running fb 2.51 on CentoOS 5.6 over the weekend end up corrupted and we had to restore from backup. No power loss to the server or anything, but noticed it when starting firebird server after our backup routine. Saw the following:

usr/lib/firebird/bin/gfix -user sysdba -pass XXXXXXX /var/opt/thgg/data/db.gdb -v -f
database file appears corrupt (/var/opt/thgg/data/thggERROR.gdb)
-wrong page type
-page 2675062 is of wrong type (expected 3, found 7)

I did some checking and saw this:
http://tracker.firebirdsql.org/browse/CORE-3549

It looks to be the same error, but it says issue is resolved and fix version is same as reported version? Not sure what this means?