Excel may be erroneously reporting the used range. I am sure this is going to sound weird, but, select all cells in the worksheet (CTRL/A); go to format, row, autofit and try again.
Else, you may have merged cells on your worksheet. If you don't know if there are, here is a macro to test test for them (courtesy contextures.com)
Sub TestForMergedCells()
Dim AnyMerged As Variant
AnyMerged = ActiveSheet.UsedRange.MergeCells
If AnyMerged = False Then
MsgBox "no merged"
ElseIf AnyMerged = True Then
MsgBox "all merged"
ElseIf IsNull(AnyMerged) Then
MsgBox "mixture"
Else
MsgBox "never gets here--only 3 options"
End If
End Sub