It doesn't totally surprise me you are having these problems. My experience has been that the Mega side of the platform, being used less, hasn't received as much attention (eg. bootloaders that don't handle the watchdog timer).
Then people compiling large arrays (in itself perfectly sensible) are probably in a minority too.
It would be interesting if, when you solve this, we document it so others can benefit from it.
Meanwhile you could always consider my suggestion of trying to store your dictionary more compactly and make the problem go away. 