Issue with insert row modal

Hello, thanks for your attention so far.

I am having an issue with the insert row modal. When I click "New" the modal appears, but the entire screen appears darkened, and as soon as I click on a field on the modal, it disappears again.

I have included a screenshot.

I would also like to only allow the user to enter values for 2 columns (in my case, item# and quantity), not all the columns. After the user enters values for 2 columns, my app will source the other columns dynamically, so they don't need to enter anything else. Is there a way to select which columns the user can enter during a row insertion?