It is also strange in this issue, too; There are differences between saying and doing. Namely, they always encourage us to join their research works, when we actually go there to join their research, however, they always say no because they don't accept students now or whatever the reason is. I am convinced that they are like this, because it happens many times to me, also I heard the same thing from other students, eg. Norweigian, Islaeli, Swedenish, Korean.
One possible reason is they believe that the earlier students decide their specialty, the better. They always ask us what specialty you are interested in. They also believe our research should be connected to our future specualty. Yes, that might be true. But how can we decide which way is good for us before we do it?
So one good thing to know is, in order to obtain a research position, say you will become that specialty, even though you are not sure about it. They will take it more seriously. Note: It gets you closer to a good position but still the firstly mentioned will sustain; they might not take you seriously enough.
Basically they don't care about students. They don't care about lecture schedule of students. They do care is only contribution to research and they follow their own rules, regadless of students' lectures.
eg.