is this normal?

[Mipam]

Hi,

I was running bind 9.3.0 on a mail system.
Recently i upgraded to bind 9.3.1 on that system.
Normally named would grow to 20 meg in size within some hours.
This is normal, this size seemed to be stable, no problems.
However, after the upgrade to 9.3.1 the size only becomes about 11 megs.
What happend to the caching part of named? Is this normal?
I don't see any crazy things happening, but still it's a big difference
running 9.3.0 and 9.3.1 looking purely at the size of bind after some 
days.
Bye,

Mipam.