The key version number (KVNO) is basically incremented when the password changes and helps catch out of sync data when they don't match. The file format your exporting to limits it to one byte so the higher bits are ignored when exported to. It should not cause a problem as data from 256 password changes ago should be long gone but might cause a problem in edge cases hence the warning.
277 = 0001 0001 010121 = 0001 0101Some reference info: https://blogs.msdn.microsoft.com/openspecification/2009/11/13/to-kvno-or-not-to-kvno-what-is-the-version/