When testing Discussion Tools at https://en.wikipedia.beta.wmflabs.org/wiki/User_talk:Kaldari?dtvisual=1, I entered {{test}} to test template transclusion (initially in source editing mode). I then switched to visual mode. The transclusion seemed to work OK, but it added an extra line break at the top. When I then switched back to source editing mode, I got the following:
<span></span> [[File:Placeholder.png|248x248px]]
... rather than {{test}} (what I expected).
Here are screenshots of the progression...
Initial source mode:
Switched to visual mode:
Switched back to source mode:
The source of the Test template can be seen here: https://en.wikipedia.beta.wmflabs.org/w/index.php?title=Template:Test&action=edit