While translating "Plants in space" I selected "spaceflight" from the source text and I was expecting a source card to appear. No cards were shown.
When trying the same on the translation text (selecting "spaceflight"), both cards (English article and missing link card) were shown, as it would be expected if the article didn't exist in Spanish.
However the "spaceflight" article exists in both English and Spanish. So I'd expect both cards to be shown when selecting the text either in the source or translation texts.