Importing Employee Time Cards for Payroll for Materials only

Our client is using Time Cards for staff to enter their timesheets.  They're using the Materials tab in the Time Card screen for staff to enter things like kilometres travelled.  These come through with the time card times into the "Import Timesheets" screen as they come into payroll as allowances. 

We've found that if the time card only has "Materials" and does not have a time entry (which happens for salaried staff who need to claim an allowance but do not need to enter a timesheet) the time card will not import into time sheets.  If the employee enters a line on the "Details" tab of the time card and leaves the hours as zero, the "material" line will then import into timesheets.

Is there something I'm missing in the setup or process to allow "materials only" time cards to be imported for payroll?  

Thank you