Tis too!
I worked on a project that ran with SQL Server. It's behavior, i.e. what it returned to a query, changed in subtle ways because of some parameter change the DBA made that did not change the tables in any way. Broke the system until resolved!
Granted this was SQL Server, but it's tough enough to deal with the idiosyncrasies of one database. And they all have their idiosyncrasies!
Alex