Cargo update ignores --precise in some cases when using `[patch]`

Problem
When [patch]ing a crate foo of version x.y.z (where x.y.z is not the most up-to-date version), running cargo update -p foo --precise x.y.z twice causes foo to be updated to the latest version (rather than x.y.z).

Steps

1. Clone libc to /tmp and downgrade to an old version (let's take 0.2.93) using: git checkout tags/0.2.93
2. cargo new foo
3. Modify foo/Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

[dependencies]
libc = "0.2"

[patch.crates-io]
libc = { path = "/tmp/libc" } # Path to our 0.2.93 version of libc

4. Run:

$ cargo update -p libc --precise 0.2.93
    Updating crates.io index
warning: Patch `libc v0.2.93 (/tmp/libc)` was not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
      Adding libc v0.2.93 (/tmp/libc)
    Removing libc v0.2.94

5. Run again:

$ cargo update -p libc --precise 0.2.93
    Updating crates.io index
warning: Patch `libc v0.2.93 (/tmp/libc)` was not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
    Removing libc v0.2.93 (/tmp/libc)
      Adding libc v0.2.94

Note that the last two lines of output are different in steps 4 and 5.

Notes

Output of cargo version:

cargo 1.53.0-nightly (65d57e6f3 2021-04-04)

It appears that without [patch] everything behaves as expected - running the same update more than once has no effect.

This may seem like an odd set of circumstances. I would be happy to explain why we run into this situation if it helps.

Reproduce the issue with the /tmp/libc checkout, the [patch.crates-io] entry in foo/Cargo.toml, and two successive cargo update -p libc --precise 0.2.93 commands. Trace Cargo's update and dependency-resolution path for patched crates, then verify that the second command keeps libc at 0.2.93 instead of restoring the latest version.