Length Of String Changes When Passed To Function

The following afterupdate procedure for my txtStart1 text box sends the value to the FormatTimeValue function that is coded in a module.

Private Sub txtStart1_AfterUpdate()
MsgBox Len(Trim(Me.txtStart1.vaue)) '<= outputs 1
Me.txtStart1.Value = FormatTimeValue(Trim(Me.txtStart1.Value))
End Sub

As you can see from the bolded text, the length of the value is 1 when outputted from the forms code.

However, when I pass it to the following function in a module it outputs 2 as the length.

Function FormatTimeValue(vTarget As Integer) As String

Dim TimeStr As String

If IsNumeric(vTarget) Then

MsgBox Len(vTarget) '<= outputs 2

Select Case Len(vTarget)

Case 1 ' e.g., user entered 1 so time should be 01:00
TimeStr = "0" & vTarget & ":00"