generator produces incorrect behavior for store method for Bit selection expression

[ilyar]

schema.tlb

_ a:(## 6) b:(a . 2)?(## 32) = BitSelection;

tlbc -qv schema.tlb 2>&1 | tee schema.txt
1549 types defined, out of them 1548 built-in, 1 user-defined
built-in type #1: `##`, arity 1; prefixes {*}; size 0..32
type #1548: `BitSelection`, arity 0, 1 constructors
  constructor `_`
        _$_ a:(## 6) b:a.2?(## 32) = BitSelection;
        begins with {*}
        size 6..38 (any bits)
                field `a`: ## 6 (used=1) (is_nat_subtype=1)
                field `b`: _1.2?(## 32) (used=0) (is_nat_subtype=0)
  type size 6..38 (any bits)
  type begins with {*}

****************
5 constant expressions:
expr #1: 6
expr #2: ## 6
expr #3: 2
expr #4: 32
expr #5: ## 32

reference behavior

tlbc -o schema-auto -n cu16::gen -z schema.tlb

bool BitSelection::pack(vm::CellBuilder& cb, const BitSelection::Record& data) const {
  return cb.store_ulong_rchk_bool(data.a, 6)
      && (!(data.a & 4) || cb.store_ulong_rchk_bool(data.b, 32));
}

generat code

npx tlb -o schema-auto.ts schema.tlb

incorrect behavior

export function storeBitSelection(bitSelection: BitSelection): (builder: Builder) => void {
    return ((builder: Builder) => {
        builder.storeUint(bitSelection.a, 6);
        if ((bitSelection.b != undefined)) {
            builder.storeUint(bitSelection.b, 32);
        }
    })
}

expect behavior

export function storeBitSelection(bitSelection: BitSelection): (builder: Builder) => void {
    return ((builder: Builder) => {
        builder.storeUint(bitSelection.a, 6);
        if (bitSelection.a & (1 << 2) && bitSelection.b != undefined) {
            builder.storeUint(bitSelection.b, 32);
        }
    })
}