title: TextBox bound to Decimal with UpdateSourceTrigger=PropertyChanged
body: <p>I've been battling this issue for a while now and seem not to be able to come up with a concrete workaround - I have a TextBox which is bound to a decimal, and the binding has UpdateSourceTrigger  set to PropertyChanged and is so by necessity (LostFocus won't work well in this case).  The default behavior while I'm sure is somehow explainable, is not acceptable for my purposes, so I've tried the following StringFormat, which I had thought remedied the issue, but only partially and am now looking for something more concrete.  My originaly fix was to add a string format to the binding...in my case it was </p>
  
  <pre><code>StringFormat={0:#.#####} 
  </code></pre>
  
  <p>so when typing something like .12345 or 1.5 the solution works great, however if I type .01234, as soon as I hit the zero key, it removes the decimal I had just typed...which for obvious reasons would be disasterous in terms of data entry.  I'm hoping that my familiarity with string formatting is just lacking.  Wost case scenario I'll have my exposed property be a string and the setter and getter just convert to decimal, but that seems like a hacky solution.</p>
  
  <p>Thanks!</p>
  
  <p>Aj</p>