Doesn't sound right. I would contact PIU. These stems should "lock" with the ground glass connection.My v2 also doesn't hold the glass stems very tightly... they fall out of the splinter if I turn it upside down. I've actually already destroyed one of stock stems like that. I bought mine at Puffitup during the 420 sale.
Also while I am at it, you should rock the stem loose as opposed to twist it out. Twisting causes more pressure on the glass. And NEVER put a cold stem in a warm Splinter. This could cause you problems as well.
You are very welcome.Shout out to Scott, @VGOODIEZ.
Thanks, bud!