I agree with that.

This server is a Solaris 5.8 server with a hudge free list (3 638 832 K right now and it stays over 1 Gb at program runtime) .

I believe the FS cache has not been tuned although i know more of this with AIX. Anyhow there is plenty of free pages to cache the data and thus descarding IO in that special case. As you say, it could have been different .