Removing 'dust cap' to fit rear spacers?

[McDub]

For the ecs 10mm and 12.5mm spacers:

http://www.ecstuning.com/Volkswagen-Golf_IV--1.8T/Wheels/Spacers/ES1990/

it says:
"Rear fitment on all MK4's requires removal of the dust cap to clear our spacer. Front fitment is not a problem."

what dust cap are they talking about, surely it's not a good think to be removing a dustcap???

i also don't get why they only mention this problem for the 10 and 12.5 sizes...

[h100vw]

It covers the hub nut, no muck can get in with the wheel on, so no big deal.

Gavin