After moving our SVN server to a completely different machine, at a different path, I just found out that all of our development team cannot merge correctly anymore.
Specifically, the problem is somewhat similar to that of this question, however this does not seem to be a path case sensitivity issue.
More into details, here is what we are currently using:
As I said, this issue is similar to the one in the linked question, however in this case I have checked the repository path in the local working copy and the path from which the merge is done, and they are identical.
I have also tried doing a fresh checkout, but still no luck: TortoiseSVN says that the working copy properties were updated, but really weren't.
When committing the merge, in fact, I do not see the property update.
If I add them manually, then all goes well.
What can I do to solve this problem, short of manually recording mergeinfo each and every time?
I'd want to thank @CiroCorvino for his help, both though comments and chat, but in the end I found the issue.
The problem seems due to the fact that we not only moved the server, but also went from subversion 1.6 to 1.8
Running the command svnadmin upgrade /path/to/repository
seems to have solved the problem, and now the subversion mergeinfo is saved correctly and automatically.