Usability problem when using multiple selection combobox

Question

I have a screen where user can select multiple values from the database. This screen follows a standard used in every screen with similar cadastre, where de data being edited or created is shown on the top, a table with the existing data is bellow and some action buttons at the bottom. So, following this standard, I've created the following screen:

In the field "Operações", the user can select multiple options, according with the tuples in the database.

As you can see, this control has usability issues. The user can't understand the field "Operações" is a multiple selection, simply looking at it. When he finally discovers it can select multiple values and save the registry, the data of the multiple selection isn't showed in a comprehensive way in the table:

Should I break the standard here? Should I use multiple checkboxes directly in the screen? What could I do to improve the usability of this screen?

Answer 1

Case 1: Where there are few options(<5) to multiselect. Then it is better to show checklist inline in tte pane, which doesn't take much screen realestate.

Case 2: Where there are many options(>5) to multiselect, Then it is better to show combobox dropdown like in:-

http://davidstutz.github.io/bootstrap-multiselect/

http://www.technomedia.co.uk/SuperBoxSelect/examples3.html

Think of showing as much options in the combo's text area as possible, if there are many options selected by the user, provide first few and state how many more options are there which can't be shown like:- "Option1, Option2, Option3, 4 more"

Above strategy can be adoption in the Grid colution also.

http://www.erichynds.com/examples/jquery-ui-multiselect-widget/demos/