I have this strange behavior in nano using the Tilix terminal (works in another terminal) where, if I paste something, the new lines are completely removed, content is wrapped and new lines are created but based on the dimensions of the terminal window. /bin/bash is selected for both terminals and I don't know what to look for any more.

For example when pasting:

#!/bin/bash
valid=true
count=1
while [ $valid ]
do
echo $count
if [ $count -eq 5 ];
then
break
fi
((count++))
done

I get:

!/bin/bash
valid=true count=1 while [ $valid ] do echo $count if [ $count -eq 5 ]; then break fi ((count++))
done

Tested both on manjaro and elementary os (ubuntu 18) and only tilix does this. Completely unusable since many of us rely on nano heavily.