Why Do Property Setters Get Called More Often Than Expected

I have observed a behaviour in VB.net where property setters get called more often than seems necessary, in conjunction with calls to the sister setter method.

Public Class Form1
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Console.WriteLine("Calling WorkReferenceTypeByReference")
WorkReferenceTypeByReference(ReferenceTypeData)
Console.WriteLine("Called WorkReferenceTypeByReference")
[Code] .....

Note the spurious call to the property setter following the method execution. I am supposing this behaviour is produced as a safety measure against inadvertently modifying the underlying property, despite this potentially being the intent. This behaviour in the case of ByRef vs ByVal usage is easily solved by choosing appropriate ByVal keyword, however hase recently noticed a more insidious behaviour, one that has caused a stack overflow of repeated calls, since the setter call would update a value that called the getter only.

Public Sub DoSomething()
Dim a As New CustomObject(anotherObject.AProperty(getterArgument))
End Sub
Public Class AnotherObject
Public Property AProperty as SomeType
[Code] .....

In the previous example, calling DoSomething() would fire the AProperty getter method, but then after that usage, would fire the setter method, which by program logic calls DoSomething() again. It is the automatic calling of the setter that puzzles me.