Cannot change the elements of certain arrays anymore.

I am not able to change the values of certain arrays of a widget anymore.
If I click on the element and change it, it just jumps back to its previous value again.
The same happens if I click somewhere else or compile it.

Take a look at the video I linked below to see what the problem is.

There is no error message appearing.

Double check localization

For some reason it did work.