Did you know that you have posted to the portion of this forum intended for reporting possible bugs? Not a big deal really, but you might have already had several people respond to your question had you posted to the FMP Pro forum, (See tab at top of screen).
What data type did you specify for the two key fields? If you are using a name (a bad idea BTW), they should both be listed as fields of type "text" when you check them in Manage | Database | Fields.
The problem with using name fields (for both companies and people) is that names are not unique and they get changed from time to time.
Imagine what might happen if "acme construction" was bought out and changed it's name to "Pinnacle Services". If you edit the name in your parent field, all the linked records that link to the original Acme construction name now disappear as you've broken the link.
It's better to use an auto-entered serial number for linking your two tables. This avoids both issues with name changes and also makes sure that he value used to link records is always unique to a specific company.