Unexpected formatting of formatted output for converted weight

[donaldpiret]

Hello,
I'm running into a bit of an unexpected behaviour with the following code:

weight = Measured::Weight.new(value, 'kg')
weight = weight.convert_to('lbs') if current_user&.prefers_imperial?
return weight.format('%.2<value>f %<unit>s')

Now I'd expect to just see this either in KG or LBS based on the user's preferences, but instead when the weight is converted, format gives me the full conversion string for the unit, eg. 319.67 lb (45359237/100000000 kg)
How do I get around this?