I have read about this phenomenon recently and came across this interesting article:
http://www.oktavamod.com/fake319.html
I have a pair of 319’s, but I bought them a while ago so I think I’m safe. I’ll have to check this coming weekend. On a side note, the Oktava mods offered on this site look very interesting. I have communicated with the fellow who does the work and one day, when I have the time and money (mostly the money) I think I’ll have mine modified.