Unable to add new record to lookup table in child record modal view

[datacate]

It's a bit confusing, so let me draw a picture:

Table A is parent to table B; When viewing a record in table A, related records from table B appear on a tab at bottom of table A record view.
Clicking the 'view' icon next to a table B record opens a modal with the details of that record. If there are lookup fields in table B, they appear with a 'view' (looks like an eyeball) icon next to them, but no 'add' ('+') icon to add a new record to the lookup table.

Now go directly to table B from the 'Home' or 'Jump To' menus, click on any record, and in the record view the lookup fields have both 'view' and 'add' icons.

Why can a record not be added to a lookup table from modal view, but it can from a regular screen view?

Thanks!
Ed

[grimblefritz]

Similar issue here.

If I open a table first and then select the add new record button, then the lookup fields show both the view and add icons.

If instead I click the + from the home page to go directly to add a new record, then the lookup fields show only the view icon.