go to "Window, tab and Field" window,
Open Field tab
Now, in fields based on a list (such as Mandatory overwrite, Updatable, ...) i can put a value (yes or no) and save.
But then, if i choose a blank value, i got an error message and record is not saved.
Log says :
15:00:05.566===========> MField.saveError: Validate - IsUpdateable Invalid value - - Reference_ID=319 - N - Y 
15:00:05.567-----------> GridTable.saveWarning: Validate - IsUpdateable Invalid value - - Reference_ID=319 - N - Y;Updatable 
I've updated my sources this morning, but can reproduce it on 1.0b.
First I thought this is identical to but it was not. I have no clue how this issue was introduced and what has to be rewinded. I tried to find my own way and attach a patch to review and try out. Please be careful! These ComboBoxes are used all over the code...
I changed ValueNamePair.getID(). The similar method KeyNamePair.getID() (which implements the same interface) does it in a similar way so I hope I did not break anything.
I've integrated your patch in my local instance (launched from Eclipse). I will report if I found something strange