As the first crate in the listing (ugh, sorry!), Encoding 0.3 was in the development since early this year (I think) and I had a fix to the warning in the issue list but didn't realize that the 0.2 branch would have the same problem. This is also partly because I haven't set the warning to fail the CI test---but if I had a separate branch for 0.2 I wouldn't be able to see that as new Rust releases do not trigger CI anyway. (So, essentially, same to a pre-1.0 situation.)
I've taken this incident as an opportunity to actually apply the fix to 0.3 branch and also published a quick fix as 0.2.33. Still have to think about the long-term maintenance though...