Tax amount on 'other amount field' - not being added

When you Configure a Contribution Page with tax that applies to the 'Other Amount' field it is not applied.

Note that the way the page appears I feel like the amount entered should be treated as inclusive rather than exclusive - the alternative would be to improve the messaging to make it clearer on the page but it feels weird to ask people to enter a tax-exclusive amount

Screenshots from 5.60 with odd currency formatting configured

Note tax is still $15

In the final screen the tax is ... interesting

Note

1. there is code to say that if the membership recurs then the other amount should not be included