In order to understand the next section, some understanding of copyright law is required. The assertions made in this section are not legal opinions; they are merely approximations of the law, based on my understanding of it.
By default, whoever creates a work owns copyright over it. This means that by default, that person is the only person in the world who has the legal right to make copies of the work.
Copyright over a work usually covers all direct derivations of this work. For example, if someone owns the source code to a computer program then they also own any direct derivations such as the binary executable.
More than one person may own copyright over a work. If this is the case, then the work cannot be copied without the permission of all of the people owning the copyright.
A person (or group) owning copyright over a work can license the right to make copies of the work to anyone he likes under any conditions he likes.
If a work is modified, the result is called a derived work.
If copyright on a work is owned by A is the work is modified by B, copyright on the derived work is owned by both A and B.
Copyright is not ownership over particular configurations of information, but rather is the right to restrict the copying of information derived from particular sources. For example, if two people point their cameras out a window and take identical photographs, each person has the right to restrict the copying of their photograph regardless of the fact that the other person has copyright over an identical photograph. In the unlikely event that two people wrote novels that were letter for letter identical and it could be proven that there was no contact between the two people when they wrote the novels, then copyright law would each protect the right of each person to restrict the copying of the novel originating from them. In practice, the probability of such an event occurring is so low that the law assumes that if two works are close or identical, that there has been some information interchange at some point.
Thus, if I own copyright on computer program X, and I create an identical copy of X called Y and distribute it under the terms of a license agreement, then that license agreement does not cover the copy X. Once the license agreement is signed, there is nothing I can do to undo the license; Y has gone. However, I still have total control over X.
Version 2 of the GNU General Public License (under which FunnelWeb is released) specifies (in a nutshell) that software can be copied freely so long as it is not sold, and that it can be modified and copied freely so long as the modifications are logged and it is not sold. In both cases, it requires that the result of the copy or modification operation be copied only under the conditions of the license.
Once a declaration is issued licensing a copy of a program under GNU license, that license cannot be retracted.