8.3 system.db.runPrepUpdate not throwing

Ignition
1 
Ignition 8.3.3, 'ACME' is a valid db connection.
Microsoft SQLServer db driver.
There is no table x, y, or z.

This throws an exception as expected:
    query = 'select y from x where z is null'
    system.db.runPrepQuery(query, [], 'ACME')

Specifically, it passes back:  Invalid object name 'x'.

This does not return an error of any kind:    
    query = 'update x set y=1 where z is null'
    system.db.runPrepUpdate(query, [], 'ACME')

Any ideas?
-Shane