Still haven't answered my visibility question - but figured out the brilliant bug I implemented which caused me to question things.  I have a primary key defined as a Smallint and an associated generator.  You've probably already know what's coming...

 

This table has a high amount of inserts/deletes.  Which rapidly increments the generator...which results in overflow errors.  So...note to self:  Either use a generator-based primary key sized to accommodate the traffic, or don't use a generator - use a composite PK which is sufficiently unique.  Adding a dedicated unique field for PK's may be elegant...but has issues for high traffic.  Which I would have figured out if I'd thought it through...