I don't think so - I'd rather say that what you've said, Nestor, is also true for British English as "Knickers" themselves are plural indeed but "a pair" in the phrase "a pair of Knickers" is singular though - that's why "a pair of" is used: to avoid misunderstandings.
"My knickers are lost" but "A pair of Knickers is lost" "My shoes are lost" but "A pair of shoes is lost"
This is very complicated indeed. Please help to clarify it, otherwise it might lead to a serious misunderstanding.
If I say "a pair of shoes is lost" you imply 2 shoes are lost, don't you? If I say "a pair of knickers is lost". How many knickers am I supposed to have lost? 1 or 2?
I found a usage note in American Heritage Dictionary which is clarifying the discussion that I have started. I would like to share it with you. Any other comments would also be helpful:
USAGE Note (Pair) Pair as a noun can be followed by a singular or plural verb. The singular is always used when pair denotes the set taken as a single entity: This pair of sh
You see, u didn't get it right either. I'd leave the shop with two pairs. The ones I was wearing before entering the shop and the ones I bought in the shop. It would make two pairs of knickers according to my calculations.