I've run the code you've given in perl 5.8.5, and I've got what I've expected anyway:

'%d' output          : 0042
'%d' output (with +0): 0042
'%f' output          : 0042
[download]

so %d does numericize for me.

Also you might want to try "%04d" instead of "%4.4d" which should have the same or similar effect.