QTextEdit: when pasting into a code block, the format is lost

If you set properties like QTextFormat::BlockCodeLanguage and QTextFormat::BlockCodeFence on a block to create a code block interactively, and then paste some code into it (control-V), the properties are lost. The clipboard text may have its own formats (for example if you paste from Creator, Konsole etc., it's not just plain text).

But even if you manage to paste without losing the block format on the first line, it's still lost on subsequent lines. So in practice the user needs to reselect the text and apply the code block style afterwards, assuming the application has a style combobox.