SMC DA 18-55mm Zoom

Possibly a silly question, and certainly trivial, but I've noticed that all my digital zoom lenses (Panasonic, Pentax, Sigma) are shortest (physically) at the wide end of their range and extend as you zoom. Apart from the 18-55mm, which is shortest at 35mm and extends as you get shorter or longer.

Anyone know the reason for this? I assume Pentax chose this configuration for a reason.

There are some other exceptions. My Sigma 24-70 is shortest at the long end - well, at about 65mm to be more precise.

The Pentax DA 12-24 is shorter at 18 than 12 or 24mm.

It all depends upon the type of lenses used and their location within the objective.

Well, yes, I'd guessed that. What I was wondering was why they had gone for that particular configuration. To avoid an inconvenient physical length if they went for the 'usual' one? Better quality?