Records seem limited to 999 when selecting from inside same table

[Marc_Dillon]

I’m working with a data table with over 7000 rows, table called “main”.
I create a new virtual column in that table with the expression
COUNT(main[_RowNumber]).
It returns the number 999.
I create a new virtual column in a different table with the same expression, it returns the actual count of number of rows; 7,000+
What is going on here?

This oddity is breaking a feature that I’m trying to implement because it means I can’t run a SELECT expression over the entire table from inside of that table.