In Part 5, 6.3.2. ServerCapabilitesType it says

"The MaxByteStringLength Property indicates the maximum number of bytes in a ByteString supported by Variables of the Server. It also specifies the default maximum size of a FileType Object’s read and write buffers. Servers may override this setting by adding the MaxByteStringLength Property defined in Part 3 to an individual DataVariable or FileType Object."

However, the MaxByteStringLength property is not mentioned in the definition of FileType (Part 5, C.2 FileType ) and also not mentioned in the definition of the Object NodeClass, as in Part 3, Table 11.
It is defined for the Variable NodeClass, as in Part 3, Table 13.

Therefore, it is unclear whether a client should look for this property, at instances of FileType.
See also Mantis 2979, where the use case was discussed and it was decided to change Part 5. Apparently it was forgotten to change Part 3.

Easiest solution:
Add MaxByteStringLength as optional Property to the definition of FileType.
I think this would be the best way to go, since the use case where we have a problem with the spec, is really only for file transfer.

Alternative solution:
Add MaxByteStringLength as optional Property to the Object Nodeclass.