Are these Lookup fields? If so... bear in mind that the Lookup table
field type is of VERY limited utility and a source of much confusion.

Your table *looks* like it has the reference name in it. However, it
does not: it has a concealed numeric ID. If you try to sort on the
reference name, or export it, or use it in another query, IT'S NOT
THERE - what's there is the ID.

Table datasheets are of *very* little use; they're good for design and
debugging but very little more. Forms (with Subforms, see below) are
much more effective for data entry and editing.

You're assuming that creating a record in Main *SHOULD* create a
record in JnxTbl. *It shouldn't*. A record in the junction table
should be created when - and ONLY WHEN - you are explicitly going to
link a record in Main to a record in RefMain.

The simplest way to do this is to use a Form based on Main, with a
Subform based on JnxTbl. On this Subform you would put a combo box
based on RefMain; the subform's master/child link field would be the
Main table's Primary Key and its corresponding foreign key. Thus when
you select a related record from the combo, a new JnxTbl record is
created (but only then).

Again... don't use table datasheets. They'll get you from A to B, or
(with some of these new features) all the way to D if you really
stretch. If you want to get any further, use a Form instead.

                 John W. Vinson[MVP]