Let $X$ be a smooth projective curve over $\mathbb{C}$ and Let $G$
be a complex reductive group. By a parahoric group scheme $\mathcal{G}$
over $X$, I mean a smooth group scheme over $X$ whose restriction to
an open set $U$ is the constant group scheme $U \times G$ (or 
$\mathcal{G}_{K(X)} \cong spec(K(X)) \times G)$ and for $x \in X - U $,
if $\mathcal{O}_{X,x}$ is the completion of the local ring at $x$ and
$K_x$ its fraction field, then 
$\mathcal{G}(\mathcal{O}_{X,x}) \subset \mathcal{G}(K_x)$ is a parahoric
sub-group  in the sense of Bruhat-Tits. I am interested in the case when
these local parahoric subgroups are just the Iwahori or the inverse image
of a fixed borel subgroup $B \subset G$ under the evaluation maps
($G(\mathcal{O}_{X,x}) \rightarrow G(\mathbb{C})$). Is it true then that
$$
   B \subset \mathcal{G}(X)?
$$
or if not is there a description of the groups $\mathcal{G}(X)$?.