Inferred type proc calls don't compile

[amylizzle]

/proc/RunTest()
        var/matrix/M1 = new()
        var/matrix/M2 = new()

        (M1 * M2).Multiply(1)

Fails with message Unknown identifier "Multiply"

[ike709]

To add some context, I believe this compiles as (M1 * M2):Multiply(1) in BYOND