Here is my case, before I studied my master´s degree I managed to write a research paper jointly with a Professor (not from my university) on databases. After that I pursue my master´s degree in CS, but on neural networks rather than databases. The thing is that I would like to do my PhD in databases with the professor I wrote the research paper with. Do you think that I can have problems with the admission committee? I would not like to go to study a PhD without any financial support at all.
I don't see why there should be any problem with this whatsoever. It is quite common for students to move around topics, particularly if you are switching between programs or universities. If everybody agrees that you are a good candidate for the position in question, then it shouldn't really matter too much that the topic is not an exact match.