VB ComboBox Requires 2 Mouse Clicks to Select Index? - vb.net

Question

For some reason with this combobox I have in my code, when I run the program, it does not change the Selected Index with one mouse click. Instead, I have to select the drop down of the combo box again, and then select the index. Any ideas on what is going on here? Here is my code, I've tinkered with it for hours.
Public Class Form1
'Mod-level variable
Dim TransactionList As New List(Of Transaction)
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.Text = "Mike Smith's Bank Account"
Lb1.Visible = False
Lb2.Visible = False
Lb4.Visible = False
Tb1.Visible = False
Tb2.Visible = False
SubmitTransactionButton.Visible = False
TransactionListBox.Visible = False
End Sub
Private Sub Cb1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles Cb1.SelectedIndexChanged
If Tb1.Text = "" Then
Tb1.Text = "0.00"
ElseIf Cb1.Text = "" Then
Lb4.Visible = False
LbAction.Visible = False
Lb1.Visible = False
Lb2.Visible = False
Tb1.Visible = False
Tb2.Visible = False
TransactionListBox.Visible = False
SubmitTransactionButton.Visible = False
ElseIf Cb1.Text = "Credit" Then
Lb4.Visible = False
LbAction.Visible = False
Lb1.Visible = True
Lb2.Visible = True
LbAction.Visible = False
Tb1.Visible = True
Tb2.Visible = True
TransactionListBox.Visible = False
Lb1.Text = "Enter Credit Amount"
Lb2.Text = "Describe the Income"
SubmitTransactionButton.Visible = True
ElseIf Cb1.Text = "Debit" Then
LbAction.Visible = False
Lb1.Visible = True
Lb4.Visible = False
Lb2.Visible = True
LbAction.Visible = False
Tb1.Visible = True
Tb2.Visible = True
TransactionListBox.Visible = False
Lb1.Text = "Enter Debit Amount"
Lb2.Text = "Describe the Expense"
SubmitTransactionButton.Visible = True
ElseIf Cb1.Text = "Display Transactions" Then
TransactionListBox.Visible = True
Lb4.Visible = False
LbAction.Visible = False
Lb1.Visible = False
Lb2.Visible = False
Tb1.Visible = False
Tb2.Visible = False
SubmitTransactionButton.Visible = False
For Each transaction In TransactionList
TransactionListBox.Items.Add(
String.Format("{0}: {1:C}. {2}",
transaction.Type,
transaction.Amount,
transaction.Description))
Next
ElseIf Cb1.Text = "Display Balance" Then
Lb4.Visible = True
Lb1.Visible = False
Lb2.Visible = False
LbAction.Visible = False
Tb1.Visible = False
Tb2.Visible = False
TransactionListBox.Visible = False
Lb4.Text = "Current Balance: $"
End If
End Sub
Private Sub SubmitTransactionButton_Click(sender As Object, e As EventArgs) Handles SubmitTransactionButton.Click
Dim transactionTypeString As String = Cb1.Text
Dim transactionDescriptionstring As String = Tb2.Text
Dim transactionAmountDecimal As Decimal
If Tb1.Text IsNot "" Then
'Tb1.Text = "0.00"
Tb2.Text = ""
Cb1.Text = ""
Lb1.Visible = False
Lb2.Visible = False
Tb1.Visible = False
Tb2.Visible = False
SubmitTransactionButton.Visible = False
End If
Try
transactionAmountDecimal = Decimal.Parse(Tb1.Text)
TransactionList.Add(New Transaction(
transactionTypeString,
transactionAmountDecimal,
transactionDescriptionstring))
Catch FormatExceptionParameter As FormatException
transactionAmountDecimal = 0D
End Try
End Sub
End Class
Public Class Transaction
Public Sub New(type As String, amount As Decimal, description As String)
Me.Type = type
Me.Amount = amount
Me.Description = description
If Me.Type = "Credit" Then
Me.Amount *= -1
End If
End Sub
Public Property Type As String
Public Property Amount As Decimal
Public Property Description As String
End Class