The character '8' should map to 0xF8 and the character '9' should map to 0xF9. This problem can be fixed by downloading a new EBCDIC character map:
http://www.bpsoft.com/support/patches/3.11/EBCDIC.map
Please download the EBCDIC.map character map file and place this file in the CharMaps directory within your Hex Workshop program directory. In many installations, the target path will resemble: C:\Program Files\BreakPoint Software\Hex Workshop 3.1\CharMaps\