Set "Cash Discount Tax Reduction" to "Always"
Create an invoice with a tax line
Set Payment term to "2/7 Net 30" [1]
Go to "journal items" tab
Early payment discount lines are set correctly
Set payment term to "30 Days", Save
Set Payment term to "2/7 Net 30", Save

Issue:
An extra tax line appear in journal items because an old tax line was
not deleted and a new one is created

[1] Payment terms: 30 Days, 2% Early Payment Discount under 7 days

opw-3285534

closes odoo/odoo#120014

Signed-off-by: William André (wan) <wan@odoo.com>