In the Definition 8.5 of the paper "integral $p$ adic Hodge theory" by Bhatt-Morrow-Scholze, they define the adic generic fiber of a small affinoid smooth formal scheme $\textup{Spf}(R)$ as $\textup{Spa}(R[\frac{1}{p}],R)$, here $R$ is a smooth $\mathscr{O}_{\mathbb{C}_{p}}$-algebra which admits an \'etale map to the formal torus. However, the adic generic fiber defined by Huber should send $\textup{Spf}(R)$ to $\textup{Spa}(R[\frac{1}{p}],R[\frac{1}{p}]^{\circ})$, here $R[\frac{1}{p}]^{\circ}$ means the subring of  all the power bounded elements of $R[\frac{1}{p}]$. 

My question is that why $R=R[\frac{1}{p}]^{\circ}$ ?  If $R$ is not smooth, a counterexample is $R=\mathscr{O}_{\mathbb{C}_{p}}\left \langle x,y \right \rangle/(xy-p)=\mathscr{O}_{\mathbb{C}_{p}}\left \langle x,\frac{p}{x} \right \rangle$(the semistable curve). In this example, $R[\frac{1}{p}]^{\circ}=\mathscr{O}_{\mathbb{C}_{p}}\left \langle x,y \right \rangle/(xy-1)=\mathscr{O}_{\mathbb{C}_{p}}\left \langle x,\frac{1}{x} \right \rangle$. Besides, if we consider the admissible blow up of the formal scheme $\textup{Spf}(R)$, then the ring $R$ is changed, however, it does not change the generic fiber. Or my understanding about the adic generic fiber functor is wrong?

Any idea will be appreciated.