Uint8ClampedArray rounding behaviour?

[Qantas 94 Heavy]

Currently, the ES6 spec uses ToUint8Clamp to convert the set value into a
number in a Uint8ClampedArray. From what I read of the spec, ToUint8Clamp
rounds ties away from zero (rev 22, 7.1.11):

> 6. Let f be floor(number).
> 7. If f+0.5 ≤ number, then return f+1.

However, in the WebIDL spec (4.2.5, step 3), it's specified to round to the
nearest even integer:

> 1. Round x to the nearest integer, choosing the even integer if it lies
halfway between two.
> 2. Set x to min(max(x, 0), 2^8 − 1).
> 3. Return the IDL octet value that represents the same numeric value as x.

Currently, both Firefox and Chrome round ties to even, not away from
zero. Am I reading this completely wrong, or is there a discrepancy in the
behaviour between the ES6 version and what's currently implemented in
browsers?
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