Select an item from a combobox using pywinauto

I am trying to automate a Visual Basic Application using pywinauto, with backend="win32". I am able to handle everything except selecting an item from one of the comboboxes. This particular combobox is dependent upon the selection of another combobox

Here is the code:

app.ThunderRT6MDIForm.xxxxx.ComboBox3.select("abc") # this correctly selects from the combobox
app.ThunderRT6MDIForm.xxxxx.ComboBox4.select(1) #This one gives error

And the error for the same:

IndexError: Combobox has 0 items, you requested item 1 (0 based)

Control Identifiers return :

        ComboBox - 'abc'    (L136, T206, R376, B227)
       | ['ComboBox3', 'abc co-brandingComboBox2']
       | child_window(title="abc", class_name="ThunderRT6ComboBox")
       | 
       |    | Edit - ''    (L139, T234, R356, B249)
       |    | ['abc co-brandingEdit10', 'Edit12']
       |    | child_window(class_name="Edit")

        ComboBox - ''    (L136, T157, R376, B178)
       | ['4', 'ComboBox4']
       | child_window(class_name="ThunderRT6ComboBox")
       |    | 
       |    | Edit - ''    (L139, T160, R356, B175)
       |    | ['5', 'Edit14']
       |    | child_window(class_name="Edit")

I have found a temporary workaround for this problem. I was able to find that pressing Alt + Down key opened the combobox and gave me the list. So, I have used the same logic in code as well and it worked!

 app.ThunderRT6MDIForm.xxxxx.ComboBox4.Edit14.type_keys("%{DOWN}")
 app.ThunderRT6MDIForm.xxxxx.ComboBox4.select("item")