Merging Multiple Companies for One Contact

I am trying to figure out if there is a way to merge all of the previous companies one contact has worked at and make it up to date so that they have one lead with their current company, instead of three leads that are two from their previous place of employment and also their current position.

We tested merging a lead where we had her current and previous place of employment, when we merged the two, Marketo at first had the current, up to date information for her current company but the next day it changed her company name back to the previous place of employment but kept the rest of the information from her current company.

Example:

Currently: John Smith works at ABC Company

In Marketo they are listed:

John Smith - ABC Company

John Smith - XYZ Company (previous company)

John Smith - 123 Company (previous company)