Here's an interesting quirk I noticed on my 500cm while playing around with the pre-release shutter. On every shutter mode except B, the pre-release mechanism works as intended:

- the mirror flops open
- the lens stops down to the selected aperture
- the back curtain opens
- the leaf shutter closes

In B mode, the following happens:

- the mirror flops open
- the lens stops down to the selected aperture
- the back curtain opens
- the leaf shutter remains OPEN

Here are a few more interesting things I have noticed:

- If you switch from another speed to B mode then the first pre-release will close the leaf shutter.
- If you fire when this problem is occurring, the shutter won't fire, but the aperture ring will step down 0.5-1 stop

obs: I've noticed that when in B mode it is the back curtain that interrupts exposure. Thus, the iris shutter never fires. I feel that this must explain what is going on.

Any thoughts if this is a design flaw or do I need to get my body serviced?

An extra note. I figured out that the fact that the shutter does not fire in b mode is an issue (the same problem does not happen on a newer 500cxi). Am I right to presume my body is damaged?

Sounds like you have a problem, B should not work differently than the other speeds when you pre-release.