Does someone from the DTF have the same problem as me?

[Shonisaurus]

My PNSO yangchuanosaurus is not properly maintained before it was properly supported on its two legs and on the decorated base of the set that is next to the chungkingosaurus, it happens exactly the same as what happens to my two Tyrannosaurus rex of Rebor "Killer Queen", paradoxically my PNSO giganotosaurus that at first did not stand up, it is perfectly supported with or without a base and even though its bipedal posture is quite dynamic, the same can be said about the PNSO spinosaurus that when I received it, it has stabality problems and now Holds perfectly with or without base. I do not understand anything of what happens. 

[Mirroraptor]

It is a common phenomenon for vinyl toys.
In the long-term placement, the vinyl toy will be slightly deformed, which may eventually lead to either standing instability or standing more stable.