Line items VAT box not respecting default value

How to replicate:

  1. Edit the vat_list dropdown box using the dropdown list editor
  2. Add in a new rate (0% added in my case, I already had 20% and 17.5% in there)
  3. Save the dropdown
  4. Edit the default value for the vat_list dropbox using the studio studio > line items > fields > vat [dropdown] (set to 20%)
  5. Save the dropbox value
  6. Open a new invoice
  7. Complete as necessary
  8. Add a group
  9. Add a line item - note the VAT rate

Expected result:
The default rate should be 20%

Actual result:
The VAT rate is 0%

currently line items take the the top entry of the list as the default, but you raise an interesting point.