This is found with javafx 9 b54.

Steps to reproduce:
1. run attached program ComboBoxApp.java.
2. click on the ComboBox to open the pull down menu then close it.
3. click on the Edit button. The width of the ComboBox is changed.
4. click on the ComboBox again to open the pull down menu.
The pull down menu doesn't align the combobox. Snapshot is attached.

This happens only for the first time after the width is changed.