Bart or whatever,
As you see in my above post, "Harbinger of Doom" is not the problem, just some of the other handles we have seen, and the only way to keep those out is to totally disallow handles.
As far as "mistakes" if you have a problem with me telling you why Rob and I replied about NVRAM, Im sorry. At least I did you the favor of taking the time to look up the datasheet.
With the information you have given, I can only guess what is going on, obviously the EEPROM "sees" the MSB of the address or you would have the problem after 256 bytes. I would approach the problem by writing page 1 and seeing if page 3 read that data, then writing page 3 and seeing if page 1 read that data.
Again, The EEPROM has been discussed ad nauseam and just looking down the subject list you will find entries on that subject. I am sure you will find the solution to your problem in one of those, do not forget to include SPI or I2C in your search to find the specific advice you need.

Erik (real name)