I developed my document mainly using Styles. However, just today, I cut and
pasted some text from another document and reformatted them using styles.
Then, I realised that my whole document is "using" the style "Char Char Char
etc." which came out of nowhere. My styles still exist, meaning I can select
text and reapply my styles. But after doing so, the style name still shows
as "Char Char...". Visually, my document still looks ok but it's annoying
that I can't remove this "Char Char Char..." style!

BTW, I reopened my document in Safe mode and the problem is still there.