Case simplify produces invalid BOM

[manticoreproject]

Case simplify produces invalid BOM

[kavon]

Replacing the definition of add in the above with

fun asInt a = (case a
  of Zero => 0
   | One => 1
   | Val a => a
  (* end case *))

fun add a b = Val ((asInt a) + (asInt b))

changes the number of type mismatches, but does not solve the issue

➤ ../trunk-pmlc/bin/pmlc -Cbom.check-all=true fib-datatype.pml 
***** Bogus BOM in Main after case-simplify *****
** invalid cast:(_t<D85C>#1:int) = (int)left<F8C4>#3:any
** invalid cast:(_t<D862>#1:int) = (int)right<F8C5>#3:any
** type mismatch in return from fib<F8C2>#3.3
==   expected  any
==   but found int
** invalid cast:(_t<D73A>#1:int) = (int)ans<F8D1>#3:any
broken BOM dumped to broken-BOM
bom/check-bom.sml:544.11-544.28: Fail: broken BOM

-Cbom.enable-unbox=false doesn't change this message either.