[espeak-ng:master] New Comment on Issue #853 Corruption issues with the fr voice
By valdisvi:

Cannot reproduce buffer overflow. 1ᵉʳ is pronunciated in that way because for superscript e there is no specific pronunciation set, and it is spelled out using Unicode. But for superscript r there is, and it comes from incomplete handling of automated replacement of accented/super/subscript characters in espeak-ng. As a workaround it can be patched with .replace rule for particular language.