I remember something about it coming up in some of the discussions of free lists and better behavior in this regard in 2.5, but I don't remember the details.
Under Python 2.5, my original code posting no longer exhibits the bug - upon calling del(a), python's size shrinks back to ~4 MB, which is its starting size. I guess I'll see how painful it is to migrate a gentoo system to 2.5... Thanks for the hint :)
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