unusual problem with new water heater,any opinions?

i ran a service call in october 2008 for a no hot water complaint on a 2 or 3 day old rheem power vent natural gas water heater..model # 42VP4OFW....the problem turned out to be a large amount of "flakes" had come down off of the bottom of the tank and,or,the flueway..the flakes had actually bridged the gap between the flame sensing rod and the burner which causes the control module to lock out since it cant determine whether or not a flame is present when the gas valve is open.....i cleared the flakes,brushed the bottom of the tank,and blew compressed air up through the flueway with the power vent blower on and pressure switch disconnected....i called rheem tech support,they had no explanation but requested the homeowner mail them some of the flakes for them to analyze...the homeowner mailed the flakes so that the rheem rep had to sign for the package... the rep never got back to the homeowner even though the homeowner called several times,left messages,etc...the water heater has been fine since then,no trouble...wondering if anyone out there has run into a similar problem on a new water heater...did rheem have a problem with many of these water heaters or was this isolated?..was the factory rep too lazy to get back to homeowner,,or did he not want to divulge the problem if he even knows what it is..what caused the [large] flakes in a brand new tank?...thanks in advance for your answers...........dan