On a contribution page using an "other amount" field, CiviCRM does not seem to calculate the taxes correctly.
How to reproduce:
- enable invoicing and taxes
- create a 15% tax, add it to the "donations" financial type
- create a contribution page with a few options, as well as an "other amount" field.
When creating a new contribution (online, or using the backend), CiviCRM will not calculate the taxes correctly. It might use the first option of the price options, for example.
The issue was reproduced on the demo site.
Using a "real" priceset is a possible workaround for this issue.