civicrm_line_item.tax_amount incorrectly set when using online payment processor

I might be wrong on this, but after almost a day playing around, was baffled why something would work in 4.6, and not in 4.7.9

Scenario (some steps are likely redundant)

• Enable taxes and invoicing.
• Create one or more membership type with financial type "Member Dues (not taxable)".
• Create price set, with a price set field value that creates membership(s) of above type. Give this price field value a different financial type that has taxes setup on it, and make that financial type taxable.
• Setup a contribution page, using dummy payment processor
• Sign-up a member

Expected Behaviour:
Amounts calculated correctly, and taxes are shown. More specifically, civicrm_line_item.tax_amount has this amount in it.

Actual Behaviour:
Taxes appear as zero, or presumably, if I had a different tax rate for the membership type financial type than the financial type associated to the line item. See screenshot.

Notice that total doesn't jive with details shown. $178.50 shown in "non-deductible amount", $165 if you add things up manually.

Note that I'm using a fictitious 8% GST tax rate.

Possible workarround:
I suspect that if I setup all financial types to use the same tax account, then this may workout fine.