If a website or business has multiple locations (and therefore multiple phone numbers), or multiple campaigns that are all directing to the same web page, often times this causes a phone call event to be attributed to the incorrect campaign or the incorrect business location when there are multiple tracking numbers all tracking the SAME source.
For example, suppose a business has two different locations, one in NY and a second in CA. If both of these tracking numbers are both tracking the source of "Google - Paid", then both tracking numbers are attempting to swap on the page any time a visitor comes to the site from either of these two campaigns. What might happen in this case is that a visitor calling the NY tracking number might have shown through as coming from the CA campaign.
This happens because there were 2 visitors at almost the same time. Even if both campaigns are on a completely different landing page, both numbers track the exact the same source; so when one of the visitors calls a tracking number, the call may incorrectly associate to the most recent visitor from that tracking source.
The way to fix this would be to restrict the tracking source to be specific to each campaign that you wish to track. This can be done one of two ways:
1) Restrict the tracking source down to a specific campaign. (Note: This requires auto-tagging to be turned on in Adwords/Bing or for the campaign name to be passed through the UTM parameters of your ad)
2) Restrict the tracking source by specifying which specific landing page your users will be directed to from your ads: