What's troubling is that swapping $a and $b give the same results. done without the {$a<=>$b} properly sorts the keys, as does {$a cmp $b}

I suspect the problem is that the numbers are treated as ascii, I noticed the problem that if treated as strict numbers then the numbers become floats and over-write one another in the hash, if you really need them as numbers then perhaps a conversion to hex would work.

Since looks like dates, can you avoid this and stuff them differently into the hash ?