I have the same issue.  Changing the dates or deleting the date does not change the order. 

When I create my invoices, I add the group items in the order I want to see them listed for my clients 

       1.  Billable Time

       2.  Billable Expenses

       3.  Charges - created from estimates of costs I incur that aren't billed to a specific vendor

When I print my invoices, they appear as:

       1.  Charges

       2.  Billable Time

       3.  Billable Expenses

Has QB considered whether its how the program treats the groups of items being invoiced and that the program somehow orders Estimate entries first when invoicing, then time, then expenses?  If so, is there someway to change this, because changing the date of the Estimate/Charges to one later than the Billable Time or Billable Expenses does not move it to the bottom of the invoice; it just changes its order within the subgroup of Charges.  Very frustrating