Superscript chars ² and ³ result in corrupt file

When using superscript chars with onload the output gets corrupted.
U can test this with the demo provided with the script. Just enter something like cm² and generate an ODS file.

Is there a workaround for this problem?

So I found the solution form my problem. Using strconv=utf8 solved it.

I find it strange because this was not necessary for xmlx