I have so far tried three (Peppermint, Camomile, Red Berry) out of the 8 or so flavours in the Lipton Infusions range sold by Tesco in the UK, they are all the second type and I have no reason to believe the others will be any different. I think this might well be a US vs. Europe manufacturing difference, I've never seen any of the flavours I see Americans talking about getting Lipton PTBs in. I have also been unable to source a distributor who can send me US Lipton pyramid bags in the UK.
The guy who first tried them is in the U.K., so I don't think it's as simple as a N.A./Europe thing.
I grabbed a pack just this week to try them out, but got the second type as well.
It might be more to do with stock age: if they switched manufacturing to the new bags at some point, then it's quite possible there's still old stock on the shelves. I grabbed an obscure flavour as I wasn't interested in the actual tea, but that may have been a mistake -- the more popular flavours will turn over quicker and there will be a better chance of getting new stock.
Next time I'll look for the most mainstream flavour I can find and see if I get the proper bags. Also, a big store with lots of turnover (big cities, etc.) might be a better place to check for similar reasons.