Impacted versions:
9.0c/e

Steps to reproduce:
Install hr_payroll_account.
Create a Payslip with a period earlier in the year.
Confirm Payslip

Current behavior:
"Account Date" (on accounting tab an on journal entries) is today

Expected behavior:
"Account Date" should be a date in the period (presumably the last day) as the help for this field describes.  "Keep empty to use the period of the validation(Payslip) date."

Also, filling the date in advance (while its draft) gives you the incorrect assumption that it will be honored at all.  It will not.

I will submit a pull request to fix for this shortly.

addons/hr_payroll_account/hr_payroll_account.py
_inherit = 'hr.salary.rule'
    _columns = {
        'analytic_account_id':fields.many2one('account.analytic.account', 'Analytic Account', domain=[('account_type', '=', 'normal')]),
        'account_tax_id':fields.many2one('account.tax', 'Tax'),
        'account_debit': fields.many2one('account.account', 'Debit Account', domain=[('deprecated', '=', False)]),
        'account_credit': fields.many2one('account.account', 'Credit Account', domain=[('deprecated', '=', False)]),
    }
class hr_contract(osv.osv):
    _inherit = 'hr.contract'
    _description = 'Employee Contract'
    _columns = {
        'analytic_account_id':fields.many2one('account.analytic.account', 'Analytic Account', domain=[('account_type', '=', 'normal')]),
        'journal_id': fields.many2one('account.journal', 'Salary Journal'),
    }
class hr_payslip_run(osv.osv):
    _inherit = 'hr.payslip.run'
    _description = 'Payslip Run'
    _columns = {
        'journal_id': fields.many2one('account.journal', 'Salary Journal', states={'draft': [('readonly', False)]}, readonly=True, required=True),
    }
    def _get_default_journal(self, cr, uid, context=None):
        journal_obj = self.pool.get('account.journal')
        res = journal_obj.search(cr, uid, [('type', '=', 'general')])
        if res:
            return res[0]
        return False
    _defaults = {
        'journal_id': _get_default_journal,
    }