1. Create a document "First line.Second line"
2. Select this text and insert a newline between the '.' and the 'S' (currently, using the Enter key).

Expected result: a single <pre> block with a single newline after the full stop, converting to " First line.\n Second line" in wikitext. Note that this is trivially-obvious on MW Vector due to the "border: 1px dashed #2f6fab;".

Actual result: two separated <pre> blocks (with a slug between them), converting to " First line.\n\n Second line" in wikitext.

I presume that we'll want to retain Enter as a break-me-out-of-this-context newline, and use Shift-Enter to allow insertion of the above.

Version: unspecified
Severity: normal