We prevent users from mapping to both a parent and child group as this would result in a situation in which the sum of accounts does not agree with the total of the parent.
For example, consider the situation in which Accounts have been assigned to Trade Receivables and Deposits ($2,000 each) and an account has also been assigned to Trade and other receivables ($1,000). In places where we show group balances without accounts (financial statements) the presentation would be as follows:
Trade and other receivables $5,000
Trade Receivables $2,000
Deposits $2,000
To avoid the confusion caused by having a different parent balance compared to the sum of its children, we prevent the user from assigning to both a parent and child group.

If the user assigned accounts to the parent group in the prior year file then that mapping is retained in the current year, and as such they will need to unassign the accounts in order to map them to a lower level.