Clippy reports warnings twice on suggestion errors

I tried the code from https://github.com/rust-lang/rust-clippy/issues/6234.
I expected to see one error, from the incorrect 'fixed' code, and one warning from the original code.

Instead, this happened: I saw one error and two warnings:

Original diagnostics will follow.

warning: immediately dereferencing a reference
 --> src/lib.rs:2:26
  |
2 |     ($visitor: expr) => (*&$visitor)
  |                          ^^^^^^^^^^ help: try this: `self`
...
8 |         m!(self)
  |         -------- in this macro invocation
  |
  = note: `#[warn(clippy::deref_addrof)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#deref_addrof
  = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

warning: immediately dereferencing a reference
 --> src/lib.rs:2:26
  |
2 |     ($visitor: expr) => (*&$visitor)
  |                          ^^^^^^^^^^ help: try this: `self`
...
8 |         m!(self)
  |         -------- in this macro invocation
  |
  = note: `#[warn(clippy::deref_addrof)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#deref_addrof
  = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

warning: 1 warning emitted

warning: 1 warning emitted

Meta

• cargo clippy -V: clippy 0.0.212 (ffa2e7a 2020-10-24)

Start by reproducing the example from issue 6234 in src/lib.rs and running cargo clippy, using the reported clippy version as context. Done means the incorrect fixed code still produces one error while the original code produces only one warning rather than duplicated diagnostics.