When switching with primary from additional contact the mobile number is placed into the fax field on the primary contact screen
Please note that the field labeled "Mobile" in the Additional contact screen is actually originally named "Fax".
There is a way to change the label in the GM.ini:
The Mobile field in the Additional Contact record can be relabeled for use as a Fax number or for storing other data.
To change the label of this field, please do the following:
1. Log out of GoldMine
2. Browse out to the main GM.INI file on the GoldMine server (usually found in C:\Programdata\GoldMine\ on server)
3. Open the GM.ini with Notepad
4. Include the following entry in the [GoldMine] section of the GM.INI configuration file: AddContactFaxLabel=Fax
5. File>>Save changes
6. Log back into GoldMine and test Explanation: When you select the option to "Switch with Primary", you are actually moving the data in the "Fax" field to the "Fax" field on the primary screen. So the behavior you are experiencing is expected.