I have a similar problem.
In what control do you see the number truncated ?
With a SQL Select to Firebird Database, the float field in TDBEdit show only 2 digits(60), but in TDBGrid show fine the number.(606)
For me is TDBEdit issue,
Under Lazarus 0.9.29 svn 21445. fpc 2.3.1 svn 13383.
I will do more check with the last lazarus svn for report in bugtracker.
Regards