Word count increases when i just modify a heading

I wrote a very long document, hundreds of pages including figures and let’s say 5 levels of headings. When I modify the largest heading (for that one i used a custom heading instead of heading 1, if it matters) the word count increases . why? lets say my document is 300,000 words. when i modify that heading the word count increases to lets say 300,002. and also the character increases, lets say from 1,800,000 to 1,800,004. Why?

and then i also modified font of some header and footer text and again the word count and character increased even more (again an extremely small fraction but still…), why might this be?

The very first step: reproduce bug using latest fresh/still version

already known : tdf#156054, tdf#114760, tdf#99189 …

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