While I wholeheartedly think that science is mostly methodically uniform, there are two things that seem to differentiate the social sciences (or humanities) from the natural sciences. (That would seem to put me on the side of methodical antipositivism, if one is into labeling.)
There are two distinct differences between the reality the natural sciences research and the one of social sciences study. While these differences are not immediately apparent, they are easily understandable when pointed out. They also lead to some methodological consequences that must be taken into account.
The Hermeneutic Double-Structure of Social Sciences
That fancy term has a simple explanation: Social sciences do not exist in the vacuum. When a study reports something about the society (or about people in particular or in general) people are going to learn about it and possibly react to it. When a study indicates that for example the average wage of women is significantly lower than the average wage of men people can acknowledge this and change this. In practice this means that people can read what the researchers in social sciences report and change the facts that they state. This means that at least the study of inequalities and social problems is basically trying to invalidate itself by pointing out the facts that need changing.
While this is true on societal level, it also applies (at least on some cases) on the personal level. A simple example of this is the mechanisms we use in trying to avoid cognitive dissonance. Negation is one of the more simpler techniques used. It is used mainly by children of certain age, before learning different types of coping mechanisms, but it is also used by adults, just less often and less overtly.
Let’s take an example: A child wants to get invited to a friends birthday-party. All of her friends are invited, but she is not. Later, when asked why she did not participate, she reports that she didn’t participate because she didn’t want to and that the friend in question is stupid. She has reinterpreted what has happened in a way that doesn’t threaten her self-image. What is interesting about this is that negation disappears when pointed out. When taught about negation and how it is used, people stop using it. This is basically because it is a form of self-deception that cannot continue when made apparent. It is no longer a useful coping mechanism so it is abandoned.
In larger scale this means that in social sciences observing and participating in the lives of the people researched also changes their lives. This possibility of change introduces problems of ethics in studying human subjects. The structure of two-way interaction between the object of study and the student is called hermeneutic because the people studied also interpret and apply the findings of the scientist. This may mean that they misinterpret the findings (see any newspaper headline about a new study being published), but at the very least it means that their actions are not directly prescribed by the researchers views. They learn about the facts presented to them from the researcher, but they decide what to do with those facts themselves.
This is radically different from the case of natural sciences (although some kinds of animal research comes close) where there is a clear distinction between an observer and the object of study, with only one way influence between them. While the opposite is trivially true in some cases of quantum mechanics (observation alters results), it is not true in the same sense.
The Constant Reformation of Social Reality
There is also another sense the social sciences differ from the natural sciences. While it is true that all of reality is in grip of constant change, the reality of natural sciences is not. While some changes are worthy of research, it is not the change itself the research is interested in. Natural sciences try to find unalterable truths and constants that may be used in exploring and understanding the natural world.
While this is in some sense true also of the social sciences, there is a crucial difference: social sciences are interested in the change, and their object of research is also constantly changing. The history of humanity has been a history of societal change, and it is also in some sense true that it was the Industrial Revolution that gave birth to the social sciences that we know today. The theory of social sciences cannot be unchanging, because the object of study is not. There are few unalterable laws in the reality of human existence. Not altering the theory when the object of study changes would be poor science. It is in this sense Max Weber meant that the social sciences are eternally young.
Note: This should not be understood as advocating ontological dualism. There is only one reality, and that is the reality of science (understood in the widest sense of the term).