I've seen that before on another brand of spacers too - can't remember who's it was though
they're faulty by design, but you could mod them if non returnable if you know someone with a lathe
*Raises hand*
Might of been mine, they where 20mm Delta Mics on my old orange one so that was about 18mths ago nearly.
Had the angle grinder out to make them fit. I bought them from wheel-spacers.co.uk and they claimed they couldn't be wrong. Someone has a design pattern wrong somewhere but mine where on rear drums rather then discs.
Could be something to do with mk2 ibiza suspension setting being different from front to back, golf front's, polo rears, that this might be a spacer problem 2? uneducated, non mechanical guess