changes from one line to two line breaks

Why has my project changed from a two line break when I press return to a one line break? I am compiling with multimarkdown and this matters.

Pressing Return should only ever give you one carriage return, but if we’re talking about the appearance in the editor, you may have previously had paragraph spacing set for the document or in the default formatting. In Format > Text > Spacing… you can set “before” and “after” paragraph spacing. This is just rich text formatting though that wouldn’t provide the line breaks you need for MMD, so you’re probably better off leaving that to 0 so you can see the literal spaces in the text. Toggling on Invisibles (Format > Options) will show you whether you’ve got the proper number of returns between lines or if it’s just a format setting giving you extra space.

(Meant to add, the default formatting is set in the Editor tab of Tools > Options; you can check what the paragraph spacing there is set to by choosing “More…” from the line spacing pull-down menu.)

How do I change the setting to give me two line breaks per return key stroke?