tutorial combo-box behaviour

I’m new to Vaadin and have just finished the tutorial that builds the contacts browser/editor. However, it doesn’t seem to render correctly. If I select a row in the table and then click:
‘save’ ‘edit’, ‘save’ ‘edit’, ‘save’ ‘edit’, ‘save’ ‘edit’, ‘save’ ‘edit’
, etc in the ‘person’ form below the table, then the ‘city’ combo-box grows wider and wider until it stretches across the whole width of the screen.

Does anyone know why this happens ?

this bug (#5833)