Created attachment 362017 [details]
GnuCash 2.6.14 test data file

The account information "Tax Related" is lost when opening datafiles stored with GnuCash 2.6 with 2.7

Attached is a test file that was created with 2.6.14
It includes only one account "Income" without any transactions

To see the effect open the file with 2.6 and with 2.7 and open the account edit dialog, respectively.
2.6: the account is marked as tax related
2.7: the account is not marked as tax related
(marked as tax related = grayed-out tick-box is shown as ticked)

Procedure how to mark the account as tax related:
- Start GnuCash 2.6.14 (assumption: any 2.6.x will do)
- Go to the Edit menue and select Tax Report Option
- Apply a test name and select "individual tax"
- Select account type "income" (the income accounts get listed in the list box below)
- Select an account
- Set the Account Tax Information tick-box
- Press the OK Button (the default dummy TXF Form will be applied)
- Save the the data file

After doing the same with GnuCash 2.7, opening the file with GnuCash 2.7 leads to correct behaviour, the account is marked as tax related.