I see no reason in general if $\operatorname{Ext}_P^1(4,1) \neq 0$ that, on restriction to R the four dimensional simple can't drop down and have a 2-dimensional submodule. I.e. On restriction to R it looks like:



`\begin{equation}\begin{array}{c}
  2\\ 2 
\end{array} \oplus 1 
\end{equation}`



 If you knew on restriction to KR the *only* irreducible submodule was two dimensional then this would be ruled out.