I believe some companies will take a small amount out to check the if bank account is valid the first time you use their service. After making my pledge I noticed at a cash machine the amount it said was available was slightly smaller than the amount in my account, so it looks like that it may have been the case for KS. However, the amount you pledge is not taken until 1st Dec, so nobody should be worried if they don't have the money quite yet. Heck, it's why I didn't pledge straight away, then KeithC told me how it works.
Also, always a good idea to check if you can purchase online with your bank.

I have also had my account frozen before, but that was because the bank suspected somebody was trying to commit fraud on my account, turns out it was true, but luckily no money was taken.

Ain't fun, especially when you do have stuff to pay.