Sap gui cannot save input after pressing Enter

Dear experts,

I'm using SAP GUI 7.5 Java for Mac and i'm having a big trouble. When entering field value of any table in SE16N, the input suddenly disappear after hit Enter button. The same error appear if i enter plant when creating PO. The value that i entered was disappeared.

I found that after enter field value, i need to hit TAB button before hit enter button. If i do that, i can enter value for the field. But i dont want to hit TAB every times i create PO or exicute value of table in se16N. This happened after i upgrade from 7.40 to 7.50. But when i downgrade, the same problem appear. Pleas help me to fix this problem. Thank you so much