Limited maximum number of values in reference selector-issue
The limitation in the number of selectable values in a reference selector (property 'select using' = 'drop down') might cause a loss of referenced values* in the DB. Therefore I suggest either (1) A warning when not all selectable values are selectable or (2) Making the maximum number of selectable values being editable. Would this be achievable? (*See https://forum.mendix.com/questions/4978/Loss-of-referenced-values-in-data-view-editing-a-data-grid for explanation).
This is a known issue we encountered ourselves a few times as well. Although it is true you should never encountered this case from user experience perspective, the issue is filed and scheduled as a bug.