WPF binding leak

I have been using WPF for some time, but I have not heard before now that there can be binding leaks in WPF. A few days ago some guy said that the following XAML "produces two binding leaks":

<TextBlock x:Name="textBlock" Content={Binding SomeProperty} />

assuming that there is some data context.

This sounds strange for me, so my question: is it true? And what are WPF binding leaks?