Pasting non-plaintext into code window pastes junk

[PDAHubbard]

Reproduced with Nightcode 2.6.0 on Gnome 3.22.2 (Debian 9)

If I paste any text which is not plain text (ie, if it is copy/pasted from a webpage like StackExchange), instead of getting plain text pasted into the file, I get this random string instead:

ÿþ<

Not sure what's going on here! :)