Combobox list gets cleared when 'tabbing' away and back to the combobox

[SimonC-24]

Steps to reproduce:

• 'tab' to the combobox
• select multiple items from the list with a keyboard
• 'tab' away of the combobox
• 'shift' + 'tab' back to the combobox
• type some chars to open a combobox list -> it is empty.

Also, when selecting e.g. 3 items from the list, then 'tabing' to another element on the gui (closing CB list view), only two items are selected, however, there should be 3.