Yup, it's true. I have one of the very early ones and FMJ absolutely gives it a sh(&fit!! I have to run Silvertips thru it only.
Period.
End of discussion.
FYI- I did the fluff and buff, polished the hell out of the chamber and tried every known ammo. I sent it back to Keltec not once but twice and they could not fix it. I took the advice of Goldenloki and filed down the slide hold open spring thingy. It fixed one of the problems. I finally arrived at the conclusion that Silvertips and nothing but Silvertips works.
Now, it will fire all eight Silvertips as fast as you can press the trigger.