You've missed another cause: you make a typo, you get the red squiggly line under it, and your right click and pick one of the ones offered -- but you pick the wrong one.
I've missed many causes, and that is why I wrote 'two
main causes'. But I've seen 'wicket fence' in the scientific article published in 1932, that is why I think that typo-theory is erroneous and I must reject it.
I've just noticed it. The sound denoted by 'w' in 'wicket' (/w/ in the IPA) is not a fricative. You must have mistaken it for /v/.
OK. It's an approximant. But that does not change the fact that /w/ is totally different than /p/.
Now back to the point. In medicine, there is something called 'wicket spike' and 'wicket rhythm':
Mu rhythm usually has a sharp negative peak to each wave [...] and giving it a characteristic wave shape. Because of this it was originally called 'comb' or 'wicket' rhythm (American usage, as in 'wicket fence').
source:
Clinical neurophysiology: EEG ... - Google Ksi
They are called 'wicket spikes', because their rounded shape resembles croquet wicket.
Also:
Landscape architectural graphic ... - Google Ksi
So, as you can see, there is something called "wicket fence".
So my theory is: some people call picket fence a wicket fence, because it is somehow similar to cricket wicket. At least in the UK. In the US, on the other hand, a wicket fence may look differently, like a 'wicket rhythm', or like a croquet wicket (see:
Evanston Wicket Fence - Border Concepts, Inc. - it is an American company and the word "wicket" has a different meaning).