This defect is fixed in Release 13.2 and higher. Here are the details of the defect and the workaround.
Synopsis: In v13, if you select a custom date range on the timesheet list and filter, timesheets are displayed. But if you hit the Refresh button, the dates become jumbled and an error message of Invalid Date Format appears.
Steps to Reproduce:
1. Go to Home > Timesheets.
2. Select a custom date range. For example, 8/1/12 to 8/9/12.
3. Click Filter. Timesheets are listed.
4. Click Refresh or F5.
Expected: The screen stays the same.
Actual: The dates in the date range are jumbled and an error of Incorrect Date Format appears.
Workaround: Click the date picker for each date again.