OK -- I might not be correct here - but from my understanding here it what I would do:
1. Enter all balance sheet accounts and verify that the balance sheet reflects all NON-operating item accounts correctly.
2. Now start entering the operating items (invoices, expenses, etc. - as of today)
3. The balance sheet should now reflect the correct balances and the operating expenses and sales should show as of today for this month.
My belief is that the P&L only shows the operating figures for the period being reviewed. If you are looking at the income statement report for this month - it will only show the operating items that have occurred this month - as opposed to the balance sheet report which will show an accumulated effect.
When looking at the income statement report, it only shows the operating items (sales and expenses) that have occurred for the period being reivew (this month).
The second thing to look at would be the period you are reporting on. The Balance sheet report will give a snapshot as of today. The P&L will give you the ability to look at the report over a period of time (this month, last month, last quarter, last year, etc.)
Hope this information is useful -- hope it helps.