Dependency PropertyChanged CallBack is not firing

Hi,

I am facing a weird issue in Dependency property changed call back.

<Bing:BingMap x:Name="BingMapUC"
                              Bing:MapDP.Location="{Binding SearchText}"/>                                                            

  
where Location is a Attached Dependency Property in the "MapDP" Class.

"SearchText" is a VM property bounded to the Textbox Text's Property where this VM class is inherited From the INotifyPropertyChanged interface,  and I am also calling the notification event in the setter of the SearchText Prop.

So, whenever the user have typed "some new value", it will automatically call the LocationPropertyChanged callback function associated with the DP.

This was working fine, previously.

But now, it is not firing, when the user have typed a new value.

What my temporary fix is, I am just calling the 

"BingMapUC.SetValue(LocationProperty,SearchText)" in the code behind of the LostFocus event, (Or where ever I want it),  and now it fires the PropertyChanged event.

I am experiencing the same issue on some other Dependency Property's too.                                                                                                                                                                                                                                                                                I have no idea, why it is not working now, which was working perfect, previously.

May I kindly know, why I am facing this one and some ideas/reasons on it and how to tackle this one.

Thanks in advance. 

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NANDAKUMAR.T