Left join in query

I have a query set up with a one-to-many left join on two tables in order to
pull all records from one table (the "one" side) and the corresponding
records from another table (the "many" side), if they exist. It works well,
but only in THAT query. In other words, if I run that query, the records
show up as I want them to. But, if I then use that query in yet another
query to further manipulate the data, the only records that show up are the
records in the many table. Why and how can I fix it? I can post the query
if needed.