Slow code execution

[side_]

I have faced very strange problem with the following code:

Type C_data
D As Date
T As Double
A As String
B As String
R As Byte
C As String
PR As Double
P As Byte
End Type

Public Carray(150000) As C_data
---------------------------------------------
Count=1
Application.ScreenUpdating = False
For i = StartPos To Cnt
Cells(Count, 1).Value = Carray(i).D
Cells(Count, 2).Value = Carray(i).T
Cells(Count, 3).Value = Carray(i).A
Cells(Count, 4).Value = Carray(i).B
Cells(Count, 5).Value = Carray(i).R
Cells(Count, 6).Value = Carray(i).C
Count = Count + 1
Next i
Application.ScreenUpdating = True
---------------------------------------------

This code works ok with a workbook containing one worksheet. It takes about 15 secs for 50000 records. But on my actual workbook I have several sheets and same code for the same 50000 records is executed for more than 3 minutes. I have figured out that this is influenced by two sheets containing about 6000 cells with comments. I have removed all comments and the problem has gone. But I need those sheets with comments
Does anyone has any ideas why it happens?