GemFire Select * Query with index returns inconsistent results

Question

I have a GemFire Query, something like "SELECT * FROM /someregion WHERE fieldX IN SET('123')".

This query returns inconsistent results. For example, it will return the same record many times, etc. If I change the query to "SELECT key FROM /someregion WHERE fieldX IN SET('123')", then I get correct results. I also get correct results if I specify the column name(s) rather than '*'.

Any ideas?