Unbound DataGridView add row with checkbox error - vb.net

Question

This is a Windows forms program. I have an unbound DataGridView control with four columns; Feature ID as string, Parts as string, Flats as string and ShowOnEst as boolean. The columns were defined in the form designer and the boolean column is, indeed, set to be a checkbox with tristate set to false.
The user selects a product from a list box and this code is executed to populate the grid
grdFeat.Rows.Clear()
For i = 0 To curProduct.lstFeatures.Count - 1
With (curProduct.lstFeatures(i))
grdFeat.Rows.Add(.FeatureId, .Parts, .Flats, .ShowOnEst)
End With
Next
If AllowUserToAddRows is false, everthing is good. Setting AllowUserToAddRows to true, however, results in the following error:
FormatException
Value '' cannot be converted to type 'Boolean'.
The error is NOT triggered in my code. It's displayed in a new tab titled "No Source Available".
It seems pretty clear that the process that adds the new editing row is trying to set the checkbox to a string value, or perhaps NULL. I'm very new (a few months) to vb.net, so I suspect I'm overlooking some simple setting somewhere, but after several hours of trying to find it, I'm starting to feel a little foolish here.
I'd give you a list of things I've tried already, but it's a long one. :) I even tried to go around the issue by adding a new row manually, .add("","","",False), but that too gives the same error, even though I'm telling it what to put in the checkbox.
What am I missing? Also, can someone point me to an explanation of how that new editing row thingy works?

Answer 1

From what you explained, I have no real explanation for the problem.
A workaround may be to set AllowUserToAddRows to false before populating the DataGridView and set it to true after.

Answer 2

Found it. Hope it helps someone else...
The rows being added are uncommitted rows. To solve it, capture the row added index, set the current cell and notify that the added row is dirty:
grdFeat.Rows.Clear()
For i = 0 To curProduct.lstFeatures.Count - 1
With (curProduct.lstFeatures(i))
Dim p = grdFeat.Rows.Add(.FeatureId, .Parts, .Flats, .ShowOnEst)
End With
grdFeat.CurrentCell = grdFeat.Rows(p).Cells(0)
grdFeat.NotifyCurrentCellDirty(True)
Next
Well, with further experimentation, this isn't a total fix. The problem is still there, but at least now handling the DataError event allows me to do something with it in code. Without these lines, the error occurs before the DataError event is triggered.
Still puzzled.