I've complained about this kind of thing before, but I continue to be surprised that someone doesn't catch (and fix) these kinds of annoyances.
I was making a booking on Holiday Inns web site and had to enter my billing address. When I submitted it I got an error saying "spaces are not allowed in zip/postal codes". I shook my head and remove the space. I get another error saying the format is invalid. I read the fine print and it says you have to enter postal codes with a hyphen. Huh? Since when do Canadian postal codes have a hyphen in them?
The "funny" part is, I bet they added that explanation because people kept getting it "wrong". I wonder if it ever occurred to them to simply accept a variety of formats? e.g. postal codes with space, hyphen, or no separator.