Bug: Sometimes newlines are not preserved

[dmgolembiowski]

TL;DR - sometimes successive lines get flattened into a single line. I observed this by creating a multi-line code block originally in markdown format:

Note: Actual \` are replaced with what you'd expect, but for the sake of this issue being semi-legible this is how I'm representing it.

\`\`\`syntaxName
// comment line
things and stuff with commonly used source code glyphs like semi-colons and parentheses

// another comment line
\`\`\`

The observed problem arises where "things and stuff..." gets shoved back, concatenating with the line starting with // comment line. After that happens, seemingly most newlines get lost unless two successive newlines are used. Curiously, if two newlines are used, the full-UI pass thru yields the correct original input.