QFileDialog don't open/save immediately after choose a file

After opening a QFileDialog (not native) the known entries will be displayed. Later all real entries will be available (asynchron). I can double click on a known entry before all real entries are available, but the action isn't immediately executed. After all real files are available the action is executed. Why is the asynchron reading not broken to execute the action immediatly for the choosen file?