In the Options Dialog, the Panel "Fonts & Colors" and there the subpanel Syntax Pane relies on undocumented ActionEvent#getModifiers behavior.
The constructor of ActionEvent:
Only talks about modifier keys as parameter options:
modifiers - The modifier keys down during event (shift, ctrl, alt, meta). Passing negative parameter is not recommended. Zero value means that no modifiers were passed
The code in the panel checks for the mask for mouse button 1:
On Ubuntu 18.10, OpenJDK 1.8u191:
As the keyboard handling for the ComboBox is also explicitly coded in the panel:
Both special cases should be removed and replaced with the default combobox behavior.
The attached screenshot shows the broken state (combobox content for language does not match displayed language).