(Apologies for the potentially unhelpful title)
From mw.org:

"I discovered two issues with inserting template:

1. Previewing an edit which inserts a template (by copy pasting in the template code) fails to pick up any of the parameter values (i.e. I get shown a bunch of triple-{)
2. Doing a roundtrip via visual editor kills every single line-break and extra whitespace in the original text. But magically this allows the preview to pick up on the parameters

[...] IIRC it was Wmse:Template:Resemall (on wmse chapter wiki)

[...] I created a video showing both the issue with failing parameters, the whitespace mangling when going to VE and then the recovery of the parameters when going back to NWT.
The text which I pasted in was copied from "classic" wikitext. If copying the pre-tagged example from the template documentation NWT does not handle the linebreaks correctly BUT can detect the parameters."

(This said, I wonder if T156498: When pasting text, don't translate multiple normal spaces into multiple non-breaking spaces is related.)