Odd behaviour from tone pot

[slidincharlie (Carlo P)]

The guitar:
my '66 Guild Starfire V (see thread below), wired with the hot lead from the pickups going to the center lug of the volume pots, like stock.
The problem:
the sound of the neck pup gets thinner and weaker (instead of getting darker) when I roll off the neck tone pot. This happens now with a new 300k tone pot as it happened with the old (500k?) pot.
This does not happen with the bridge pup.
The neck and the bridge pup/pots assemblies are identical.
The tone cap is a .022 orange drop.

Any advice is highly welcome...

[slidincharlie (Carlo P)]

An update:
the neck tone works normally when both pups are engaged. It works oddly as described only when the neck pickup alone is engaged... :-/

[slidincharlie (Carlo P)]

I've found that the neck pickup has got something wrong: it reads 0.L (open?) on my DMM.
It sounds apparently normal (maybe brighter than expected, but not weak); could this apparent internal problem be the cause of the odd behaviour of tone pot describd above?