When trying to save a file with, for example, "50%" in its name, it becomes "50_".
In recently solved T45900 it was said that symbols from this wiki article are now automatically replaced with underscore. I can understand why we replace something like "|", ">", etc. These symbols are not supported on Windows, so replacing them with underscore increases compatibility.
However, I think "%" symbol was included by mistake. That wiki article mentioned it because it was used for something in RT-11, but it is deprecated OS with even more deprecated file system with 6.3 file names (even worse than 8.3 format in DOS); also, it was flat file system with no support for subdirectories and it did not support many other common symbols. I do not think that limitations of RT-11 file system have any meaning for modern software including Blender.
Feel free to close as invalid if I'm wrong and there is actually a modern file system where "%" is not supported (in that case please tell what is it), otherwise please fix this.