Error trying to modify perm space.

Database
Enthusiast

Error trying to modify perm space.

Example:

SEL SUM(maxperm),SUM(currentperm) FROM dbc.diskspace WHERE databasename = 'rdf_refresh';

Sum(MaxPerm) Sum(CurrentPerm)
99,999,999,968 0
/*********************************/

MODIFY DATABASE rdf_refresh AS PERM = 0;
MODIFY DATABASE Failed. 3541: The REQUEST TO assign NEW PERMANENT space IS invalid.
/*********************************/
Note: Database DBC currently has negative perm.

I can accomplish this in 2 steps.

MODIFY DATABASE rdf_refresh AS PERM = 1e9;
MODIFY DATABASE completed. 4 rows processed.

MODIFY DATABASE rdf_refresh AS PERM = 0;
MODIFY DATABASE completed. 4 rows processed.

Why would this fail to modify to 0 in one query?

Thanks, Robert Glass