UTF-8 e-grave issue with option -K, caption path

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OS: GNU/Linux feh version 3.9, Compile-time switches: curl exif inotify help magic verscmp xinerama

Command feh -K caption ./feh.png with caption text « è » saved to file ./caption/feh.png.txt shows:

The correct result would be a black rectangle with « è » as the caption. Data files: test-caption.tar.gz. The caption file is UTF-8 encoded.