title: NSLayoutConstraint errors only when switching view controllers
body: <p>I'm getting some very weird behaviour from one of my view controllers.</p>
  
  <p>I'm navigating to the same controller (with different instances of it) from two different <code>UITableViews</code> in different tabs.</p>
  
  <p>When it gets displayed from a tap on a <code>UITableViewCell</code>, everything is fine and no errors display. If I have the controller open and I navigate away from it by selecting another tab, then navigating back to it through pressing the original tab, I get a large amount of <code>NSLayoutConstraint</code> errors.</p>
  
  <p>I don't actually have any constraints in my cell and I don't have any UI elements on the cell's content view in the Storyboard, as I'm adding all of them programmatically. I'm not defining any constraints in the code either.</p>
  
  <p>The full error is <a href="http://pastebin.com/VG4jUK9t" rel="nofollow">here</a>, as it's too large to reasonably paste into SO.</p>
  
  <p>An excerpt is as follows:</p>
  
  <pre><code>2015-04-11 16:49:23.889 TradingPost[6982:60b] Unable to simultaneously satisfy constraints.
  Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
  (
  "&lt;NSLayoutConstraint:0x155e5250 H:[UILabel:0x155d8150(158)]&gt;",
  "&lt;NSLayoutConstraint:0x155ed9e0 H:|-(8)-[UILabel:0x155d8150]   (Names: '|':UITableViewCellContentView:0x155d4a80 )&gt;",
  "&lt;NSLayoutConstraint:0x155eda30 H:[UILabel:0x155d8150]-(47)-[UIView:0x155e01a0]&gt;",
  "&lt;NSLayoutConstraint:0x155f1bc0 UIView:0x155e01a0.trailing == UITableViewCellContentView:0x155d4a80.trailing - 8&gt;",
  "&lt;NSAutoresizingMaskLayoutConstraint:0x156b7640 h=--&amp; v=--&amp; H:[UITableViewCellContentView:0x155d4a80(0)]&gt;"
  )
  
  Will attempt to recover by breaking constraint 
  &lt;NSLayoutConstraint:0x155e5250 H:[UILabel:0x155d8150(158)]&gt;
  
  Break on objc_exception_throw to catch this in the debugger.
  The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in &lt;UIKit/UIView.h&gt; may also be helpful.
  </code></pre>
  
  <p>Addition: Upon further investigation, I find I'm still getting errors, even when I remove all UI generating code from the controller and all constraints from the Storyboard. At this point I'm suspecting witchcraft.</p>