Size-type error after pass simplify

[FluxusMagna]

I get an error due to some kind of size-type problem. One part has reduced the expression 10+10+10 to 30 and another hasn't, which creates a mismatch even though they are indeed the same.

Error:

Type error after pass 'simplify':
In function lifted_triangle_5340
When checking function body
When matching declared return type to result of body
Type error:
Type annotation is
  {[d<{(+) ((+) 10 10) 10}>_6693]f32}
But result returns type
  {[30i64]f32}

Code to replicate:

type v3= (f32,f32,f32)
type v4= (f32,f32,f32,f32)
type C4N3V3 = (v4,v3,v3)

let serializeC4N3V3 (((r,g,b,a),(nx,ny,nz),(vx,vy,vz)):C4N3V3)  = [r,g,b,a,nx,ny,nz,vx,vy,vz]

let triangleMeshC4N3V3 [m][n] (vs:[m][n]C4N3V3) : []f32 =
    let triangle v0 v1 v2 = serializeC4N3V3 v0 ++ serializeC4N3V3 v1 ++ serializeC4N3V3 v2
    let quad v0 v1 v2 v3 = triangle v0 v1 v2 ++ triangle v2 v3 v0
    in tabulate_2d (m-1) (n-1) (\i j -> quad vs[i,j] vs[i+1,j] vs[i+1,j+1] vs[i,j+1])
    |> flatten |> flatten

entry particleSystemMesh [m][n][k]
    (vs:[m][n]C4N3V3)
    (coords:[k]v3)
    : []f32
    =  map (\_ -> vs) coords
    |> map triangleMeshC4N3V3
    |> flatten

[athas]

I can reproduce. This is just some simplification error in the core language.