Failure to match when a number is followed by a %

I have some asm syntax which allows something like this minimal reproducer to occur, but it fails to compile with a no match found error.

#subruledef a
{
    s{x: u4} => x
}

#subruledef b
{
    %r{x: u4} => x
}

#ruledef
{
    {x: a} {y: b} => x @ y
}

s0 %r0

Changing the rule def and instruction to the following lets it compile successfully.

#ruledef
{
    {x: a}, {y: b} => x @ y
}

s0, %r0

The issue still occurs with --debug-no-optimize-matcher

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