It doesn't sound normal.
Is it a known issue ? Can it damage the sheevaplug ?
1. It's not normal.
2. No. First time I've heard of it.
3. It's not my area of expertise, but AFAIK it's more likely to be a power supply component than a computer board issue.
Regardless, you should contact
jason@newit.co.uk (if you bought it from us) with your original order details.