I'm using coverxp, dragging in hi-res cover scans, printing on 8x14 paper.

When I trim the printed covers (no, I'm not cutting off part of the cover) they seem to be just a bit short, width-wise.

It's not a big deal, really - but I was just wondering if this is normal.

Same damn thing happens to me as well! I've tried every setting with my crappy printer (HP Deskjet 648C) but to no avail.
Sorry I don't have an answer for you, but wanted to let you know it's not just happening to you.

Have you verified that your covers are properly sized? Here is a list of all the correct dimensions for each size cover:

INSERT: 4.833 x 7.00” or 1450 x 2100 pixels
STANDARD SINGLE: 10.80 x 7.25" or 3240 x 2175 pixels (spine: 170 pixels)
ALPHA DOUBLE: 11.017 x 7.25" or 3305 x 2175 pixels (spine: 235 pixels)
ALPHA TRIPLE/NEXPAK SLIM 4: 11.28 x 7.25" or 3384 x 2175 pixels (spine 314 pixels)
ALPHA 4/5 DISC: 11.693 x 7.25" or 3508 x 2175 pixels (spine: 438 pixels)
ALPHA 6/7 DISC: 12.203 x 7.25" or 3661 x 2175 pixels (spine: 591 pixels)
THINPAK SINGLE: 10.50 x 7.25" or 3150 x 2175 (spine: 80 pixels)
THINPAK DOUBLE: 10.60 x 7.25" or 3180 x 2175 (spine: 110 pixels)
SLIM 6: 11.233 x 7.25” or 3370 x 2175 (spine: 300 pixels)
SLIM 8: 11.317 x 7.25” or 3395 x 2175 (spine: 325 pixels)
SLIM 10: 11.533 x 7.25” or 3460 x 2175 (spine: 390 pixels)