Scenario:

Project A has been around for a while and it is licensed using Apache 2..

Large Project B will use and possibly redistribute Project A as well as a contributor's certification agreement (CLA) (not copyright transfer). Project B will offer you it's works underneath the GPL so that as proprietary software.

Where does that leave project A, which you will see two versions? Will the relevant license just be a purpose of which project a person downloads the code from?

It isn't obvious who the copyright owner(s) in project A are, nor who's filling out the CLA, and if the copyright holder(s) is/would be the person(s) filling out the CLA.

The easiest choice is that project B distributes project A's code underneath the Apache 2 license, although ongoing to distribute the relaxation of it's code as GPL. This really is quite possible, because the licenses are compatible, presuming it's GPLv3. (See http://www.gnu.org/licenses/license-list.html )

If project B makes modifications, they would probably be licensed only underneath the GPL (based on exactly what the CLA) states. This could mean individuals modifications could be useless in project A, unless of course the copyright owner also made a decision to lead these to project A underneath the apache 2. license.

A little more details allows a clearer response to be produced.