The state site you linked to is interesting. It says:
"Employers who choose to withhold premiums from their employees may withhold up to 63.333% of the total premium. The employer is responsible for paying the other 37.667% and remitting total premiums to ESD on a quarterly basis starting April 2019."
This will be interesting, because 63.333% and 37.667% adds up to 101%.
It'll be loads of fun to watch you WA employers try to figure this one out.
It also says,
"Under the law, employers may split the cost of the program with employees by withholding up to 63.333% of the premium from their paychecks."
Maybe it's a display issue and QB internally will calculate it as you expect.
If QB will only put 63% f the 0.4% against the employee you'll still be OK legally.
It's true you may not be able to hit your employees for that last .333% of .4%.
If you have more than 50 employee and a $2,000,000 annual payroll you'll be out $26.64.
If you have fewer than 50 employees it looks like you don't have to pay at all as a company.