Fieldname "On" causes parse failure?

[ollie1400]

Trying to parse a file with a field called on anywhere in it causes a crash:

For example trying to parse the file containing:

On: 2

results in:

Error using char
Conversion to char from logical is not
possible.

Error in ReadYamlRaw>scan_map (line 180)
        ich = char(i);

Error in ReadYamlRaw>scan (line 118)
        result = scan_map(r);

Error in ReadYamlRaw>load_yaml (line 78)
            result =
            scan(yaml.load(fileread([filename,
            fileext])));

Error in ReadYamlRaw (line 42)
    result = load_yaml(filename,
    nosuchfileaction, treatasdata);

Error in ReadYaml (line 48)
    ry = ReadYamlRaw(filename, 0,
    nosuchfileaction, treatasdata);

I've tried variations on the input file and it really just seems to be the presence of the word on.