GUI:Popup not closing



i have added popup to textbox control in my MVVM application and TextBox.Text property is Bound to a Variable declare in View-model. The problem is, when i set value in ViewModel then Popup control opens automatically with filtered by newly assigned value. if i have 5 TextBoxes on single view with this popup attached then all popup gets open simultaneously when value set to all textbox in bounded variables in view-model. it looks very bad and user have to close all popups manual by selection values again.
 Also i need Free-text allowed which is not exists in popup List and i dont want to add in popup Source List. Now currently it adds new value in popup list but when i load view second time with same record then added value not exists in popup so Auto-suggest function make it blank when click on TextBox. it is more critical case in DataGrid Control.
help will be appreciated.
Rest is very nice Control and thanks to the developers.