New accounts can be made within existing account groups, based on the currently selected line in the accounts list. If the account group selected is 'closed', then instead of naming the account you'll be asked to rename the group.
Yes, I can reproduce the bug under Mac OS X. There's also a similar bug on Qt.
(from [7f31c4c20b39]) [#358] Fixed a Qt selection glitch on New Account.
(from [e1020c61a4d0]) [#358] Fix selection glitch when adding account in group (OS X).
The bug has been fixed in the latest commit.
It's another of these bugs caused by the change in the way NSOutline item references work in 10.7.