What is the version of xEdit you are using?
SSEEdit 4.0.2 (F796EF8E) starting session 2019-08-19 22:05:30

Describe the bug
TES5Edit outputs MTNM fields in RACE records that are 5 bytes in size, with a null byte, at the end.

To reproduce
Steps to reproduce the behavior:

1. Load skyrim.esm.
2. Copy DefaultRace into a new esp file.
3. Save it.
4. View the file with a hex editor.

Expected behavior
The MTNM fields should have a length of 4 bytes.

Additional context
This is a problem because it confuses other tools, when loading race records, including one I am working on at this moment.

The solution (AFAIK, I am not familiar with the xEdit codebase, nor with Pascal) would be to change

wbRArrayS('Movement Type Names', wbString(MTNM, 'Name')),

to

wbRArrayS('Movement Type Names', wbString(MTNM, 'Name', 4)),

in wbDefinitionsTES5.pas, and other such files.