Timesheet Error with custom Line Classifications in Project Server 2013

Question

We implemented Project Server 2013 last year and began using timesheets.  We are a billable consulting group.  In order manage our billing, we have created three custom line classifications, "Billable Onsite", "Billable Offsite",
and "Non-billable".  We do not use "Standard" as a line where time is entered.  We are using SEM.  We have chosen no prepopulation on timesheets.  Our system is updated through the March 2013 update.
The error we get is presented as "__error Loading" with the title bar of the pop-up reading "Message from webpage".  This occurs when you attempt to add a new line to a timesheet and choose one of the custom line classifications. 
A confusing aspect to this, while we have prepopulation turned off, the timesheet is populated with "Standard" lines for the tasks that are currently assigned to the user.  We have come up with a workaround that works sometimes but not all the
time.  When the user receives this error, they move away from the timesheet screen and then return.  They add all of the applicable lines to the timesheet with "Standard" even if they already exist on the timesheet and save.  Then
they add the lines with the appropriate line classification and the time.  If they receive the "__error loading" error again, then the timesheet can not be corrected.  You must delete the timesheet and recreate.  We have been able
to recreate the problem in a vanilla install with a custom line classification added.
Just yesterday, I was able to find a error log entry that may help some of you identify the source:
General Unhandled Exception in _TimeSheet.GetTimesheetForGridJsonFromViewUid_ Attributes:  System.ArgumentException: Assignment line already exists for assignment uid: d9afeb60-d589-e311-bd64-08edb9dd8afb     at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.VerifyLineIsUnique(Guid
assignmentUid, Guid taskUid, Guid projectUid, Guid lineClassUid)    
at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.CreateAssignmentLine(Guid assignmentUid, Guid taskUid, Guid projectUid, Guid lineClassUid, String taskName, String projectName)     at Microsoft.Office.Project.Server.BusinessLayer.TimesheetSEM.CreateAssignmentLine(Guid
assignmentUid, Guid taskUid, Guid projectUid, Guid lineClassUid, String taskName, String projectName)     at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.AddTimesheetLine(Guid assignmentUid, Guid taskUid, Guid projectUid, Guid
classUid, ValidationType validationType, Guid lineUid, String taskName, String projectName, String comment)     at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.ImportTimesheetLine(NewTask importedLine)    
at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.<>c__DisplayClass4c.<AddNewLines>b__49(NewTask line)     at Microsoft.Office.Project.Server.Library.PSUtility.Apply[T](IEnumerable`1 enumerable, Action`1 fn)    
at Microsoft.Office.Project.Server.BusinessLayer.Timesheet.AddNewLines(IEnumerable`1 newLines)     at Microsoft.Office.Project.Server.BusinessLayer.TimesheetSEM.AddNewLines(IEnumerable`1 newLines)     at Microsoft.Office.Project.Server.BusinessLayer.TimesheetLoaderForGrid.Load()    
at Microsoft.Office.Project.Server.BusinessLayer.TimeSheet.GetTimesheetForGridJsonFromViewUid(JsGridSerializerArguments gridSerializerArgs, Guid tsUid, Guid viewUid, String changesJson, String viewOptionsJson)     at Microsoft.Office.Project.Server.Wcf.Implementation.PWAImpl.<>c__DisplayClass2f5.<TimeSheetGetTimesheetForGridJsonFromViewUid>b__2f4()    
at Microsoft.Office.Project.Server.Wcf.Implementation.WcfMethodInvocation.InvokeBusinessObjectMethod(String businessObjectName, String methodName, IEnumerable`1 actions)  . Standard Information: PSI Entry Point:  Project User: i:0#.w|mayberry\nunderwood
Correlation Id: 91c4ca27-6492-e311-93ff-00155d149902 PWA Site URL: XXX SA Name: Project Services Application PSError: GeneralUnhandledException (42), LogLevelManager Warning-ulsID:0x00101622 has no entities explicitly specified.
We have not been able to find any similar timesheet issues here or on other boards.  Our users, as you can imagine, are getting increasingly frustrated.  A ny advice?
Thanks,
Nate

Answer 1

More scenario testing today. Tested with both "No Prepopulation" and populate assigned task options! no difference in our instance. We are only updated through March 2013, waiting for IT support. We have previously tried the deactivation/reactivation
of custom classifications. Tried with and without template, no difference. So the new scenario and findings:
1. Create a project with 2 tasks, one assigned and one not. Save and publish.
2. Create a timesheet, do not use an existing timesheet. Here we found, in spite of population option chosen, the timesheet was populated with a Standard line for the assigned task. With no action taken other than creating timesheet, the reporting assignment
table showed the new entry.
3. Add an assignment to the other task in the project, publish.
4. Open the same timesheet period. Now I saw the other task appear on the screen. It did not show in the database. I could not save to make it appear in the database unless I did something else to the screen to make it "dirty". Once I did that,
I could save and the second Standard line appeared In the database. 
If I tried to add a custom line class line to the TS when the Standard line was not in the database, I get the error. It doesn't matter if it shows on the screen.
If it shows on the screen but not in the db, and I attempt to add a non-standard line, it will error, unless I manually add the standard line first.  The user would not know to do this.
You will not be able to reproduce if you make the assignments and then create the TS. You need to try in reverse order.
It appears as though there are issues with both the timesheet population options and the code that runs when the TS loads after it's initial creation. I'm wondering why on creation the standard line is created and committed to the db, but on reload with
new tasks it doesn't' do the same. Also when No Prepopulation is turned on, why my time sheets are always prepopulated.
Sorry for any typos, working from my ipad keyboard. Thanks for your help!