I think I'm stumped too, but I'll offer this: the range operator in the second subscript makes me nervous:
$bigArr[0 .. 2] = $dataArr[$count][0 .. 2];
I'm not sure what context that gets evaulated in, but what you want is a list, I believe. If it's getting scalar by mistake, that could be trouble.
So I'd try either wrapping it in parens, or explicitly using a list:
$bigArr[0 .. 2] = $dataArr[$count][(0 .. 2)];
$bigArr[0 .. 2] = $dataArr[$count][0,1,2];
...and see if that helped.
In reply to Re: Why does this core? or How am I being a bonehead