title: memory leaks in Microsoft.FSharp.Control.Mailbox?
body: <p>I'm hunting for some memory-leaks in a long runing service (using F#) right now.
  The only "strange" thing I've seen so far is the following:</p>
  
  <ul>
  <li>I use a MailboxProcessor in a subsystem with an algebraic-datatype named QueueChannelCommands (more or less a bunch of Add/Get commands - some with AsyncReplyChannels attached)</li>
  <li>when I profile the service (using Ants Memory Profiler) I see instances of arrays of mentioned type (most having lenght 4, but growing) - all empty (null) whose references seems to be held by Control.Mailbox:
  <img src="https://i.stack.imgur.com/cS6lh.jpg" alt="enter image description here"></li>
  </ul>
  
  <p>I cannot see any reason in my code for this behaviour (your standard code you can find in every Mailbox-example out there - just a loop with a <code>let! = receive</code> and a <code>match</code> to follow ended with a <code>return! loop()</code></p>
  
  <p>Has anyone seen this kind of behaviour before or even knows how to handle this?
  Or is this even a (known) bug?</p>
  
  <p>Update: the growing of the arrays is really strange - seems like there is additional space appended without beeing used properly:
  <img src="https://i.stack.imgur.com/KnbgN.jpg" alt="enter image description here"></p>