Syntax Highlighting causes insertions to be copied to a new line each time Enter is pressed in WikiEditor

STEPS TO REPRODUCE

Preconditions: user has to be Advanced.

1. Edit a page in Wiki mode (make sure Syntax Highlighting is enabled from Administer Wiki > Editing > Syntax Highlighting)
2. Click on a button from the toolbar to insert something (e.g. a horizontal ruler or a heading)
3. Press Enter to move to a new line

EXPECTED RESULTS

The cursor is moved to a new line below the insertion.

ACTUAL RESULTS

If pressing Enter just after the insertion (without any clicking in the editing area), the respective insertion is copied to a new line each time Enter is pressed (screenshot attached).

However, if after the insertion is clicked in the editing area first, then pressing Enter, the cursor is moved properly to a new line.

If the Syntax Highlighting is disabled, the cursor is moved to a new line without copying the insertion.