schmittjoh/JMSSecurityExtraBundle — comment on commit 33737c5aa0ee6db07fc19b45a03ddc8c6a9fdd6a
File: JMSSecurityExtraBundle.php line 45
By stof:

you don't keep any reference to the previous security extension so you will loose the factories registered before the change.

So to avoid breaking things, this bundle must in fact be registered first in master, to be sure to do the replacement before registering any factories (and for instance, SecurityBundle registers some factories so it will break the core ones if it is registered before JMSSecurityExtraBundle)