There was a famous optiboot bug that hit at about that file size (long ago fixed.)
http://code.google.com/p/arduino/issues/detail?id=380&can=1&q=optiboot
I don't remember ever hearing about a similar problem in atmegaboot, and it's logic should be different enough that it doesn't have exactly the same error, but it could be related.
You could load up optiboot instead; it is known to be fixed, and is 1.5k shorter as well...