in logseq 0.1.9 (desktop version, windows x64): tried copying and pasting a block that includes code with a line break in it. in the pasted block the line break is removed and replaced with a - followed by a space.
also commented this info into a similar bug report at: Copy and paste to code block behavior strangely · Issue #1638 · logseq/logseq · GitHub
many thanks as always