data disappear after extracting from querytable

In worksheet("source"), there are around 10000 rows and 12 columns (fields).
All columns in worksheet("source") are going to be pasted on
worksheet("target") using the following codes. I have also simplified the
query which actually involved more complicated calculations.
Columns A to H: all rows have data
Columns I to L: the first 6000 rows are blank

The problem is that I could only extract the data from Columns A to H, but
not Columns I to L which are ALL BLANK. Also, all fieldnames from Col. A to
Col. L can be extracted correctly to row1 of worksheet("target")...
The most strange thing is that if I do not leave the the first row blank
(e.g. leave only Col. J, K & L blank, and input '1' in cell(I2), then Col. I
will be extracted correctly...

Can anyone help?
Thanks a lot!!

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Sub test()

Dim varConn As String, varSql As String
Dim varQry As QueryTable

Worksheets("target").Columns.Delete

varConn = "ODBC;DefaultDir=C:\Work;driver={Microsoft Excel Driver
(*.xls)};DriverId=790;dbq=C:\Work\testDB.xls"

varSql = "SELECT * from [source$]"

Set varQry = Worksheets("target").QueryTables.Add(Connection:=varConn,
Destination:=Worksheets("target").Range("a1"), Sql:=varSql)
varQry.BackgroundQuery = False
varQry.Refresh

End Sub