ctexheading breaks makeidx under koma-script documents

[suxpert]

How to reproduce:

\documentclass{scrbook}
\usepackage[heading=true]{ctex}
\usepackage{makeidx}
\makeindex

\begin{document}
ctex\index{ctex}
\printindex
\end{document}

Then

latexmk -xelatex

will fail generating pdf file with error:

./main.ind:1: LaTeX Error: Float(s) lost. ... l.1 \begin{theindex}

Use ctexheading gives the same error.

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It's OK if I use imakeidx, but it seems that koma-script works better with makeidx.

Environments: TeXlive in kali linux (wsl2), with ctex version 2.5.5, koma-script version 3.28.