Visual editor damages edited text

[spoko_ws]

I've written a page in internal HTML editor. When I update the page, it appears with some additional characters taken from the inside of the message. I can not force it to save exactly what I write inside, no matter how often I update the page. I'm including the whole page, such that you can reproduce the problem.

The page, which I cannot save clearly into database

It seems your external HTML doesn't conform to the requirement neither for the visual editor nor for the HTML editor. The problem is with autop: you either use it and replace all <p> tags with line breaks or you don't use it and strip all line breaks from the HTML code (as the visual editor would do).

In reality autop allows line breaks after the closing tags for block elements but nowhere else.

See also: #16239

Tested in 3.5 with Twenty Twelve. Couldn't see any additional characters. Visual, Text and preview looks the same.