@aleyx: my bad. You are right -- I didn't see the "not".
That said, the fact that the OP sees case differences in lost books implies that there is a problem doing renaming. Using a NAS is one reason this can happen. Another reason is a mismatch between the file system and the operating system. Problems like this will arise if you run windows using a case-sensitive file system, or if you run linux with a non case-sensitive file system, or if you are using a portable drive and moving it between operating systems. I don't have enough experience with macs to speculate whether case sensitivity problems might arise.
Bottom line: be sure that the file system type is native for the OS you are running, and do not move your library storage device between dissimilar operating systems.