Have found in Beta 4 that PDFs will often get ‘frozen’ in the preview pane. In other words I go to select another document and the new selected document does not appear in the preview pane.
This also happened to me when DT3b4 was initially installed. Whenever this happened, re-starting DT3b4 solved the issue temporary. BUT the issue disappeared after a few days of usage.
Thanks for the report! This should be addressed in Beta 5. Thanks for your patience and understanding.