The riddle of the disappearing WPF databinding

I'm currently on a custom control that has a bunch of panels slaved to each other via databinding. And I ran into a bug where moving an element around would suddenly break the sync with the other panels. Nothing in the Output about data-binding failing, so i inspected it with Snoop to see that my data-binding had just up and gone away. So I tracked down the suspect code and monitored the data source with Mole as i stepped through and saw that the data-binding went away right after I set the dependency property.

Yeah, not really magic at all. A quick look at the Xaml showed that I had left this particular binding as default (i.e. OneWay). And if you have a OneWay binding and manually set the dependency property, the binding gets overwritten and goes away. Switching the binding to Mode=TwoWay restored my sync.