Pin package seems not to be working

I want to pin CSV.jl to version 0.3.1 because version 0.4.1 cannot read my file.
If it is pinned, I cannot update it, as expected. However, installing another package changes the version.

(v1.0) pkg> add CSV@0.3.1
 Resolving package versions...
  Updating `~/.julia/environments/v1.0/Project.toml`
  [336ed68f] ↓ CSV v0.4.1 ⇒ v0.3.1
  Updating `~/.julia/environments/v1.0/Manifest.toml`
  [336ed68f] ↓ CSV v0.4.1 ⇒ v0.3.1
  [7d512f48] + InternedStrings v0.7.0
  [69de0a69] - Parsers v0.2.7

(v1.0) pkg> pin CSV@0.3.1
 Resolving package versions...
  Updating `~/.julia/environments/v1.0/Project.toml`
  [336ed68f] ~ CSV v0.3.1 ⇒ v0.3.1 ⚲
  Updating `~/.julia/environments/v1.0/Manifest.toml`
  [336ed68f] ~ CSV v0.3.1 ⇒ v0.3.1 ⚲

(v1.0) pkg> up CSV
  Updating registry at `~/.julia/registries/General`
  Updating git-repo `https://github.com/JuliaRegistries/General.git`
 Resolving package versions...
  Updating `~/.julia/environments/v1.0/Project.toml`
 [no changes]
  Updating `~/.julia/environments/v1.0/Manifest.toml`
 [no changes]

(v1.0) pkg> dev SingularSpectrumAnalysis
  Updating git-repo `https://github.com/baggepinnen/SingularSpectrumAnalysis.jl.git`
┌ Warning: project file for SingularSpectrumAnalysis at /tmp/tmp6mC8cD is missing a `version` entry
└ @ Pkg.Types /build/julia/src/julia/usr/share/julia/stdlib/v1.0/Pkg/src/Types.jl:700
[ Info: Path `/home/bertrand/.julia/dev/SingularSpectrumAnalysis` exists and looks like the correct package, using existing path instead of cloning
 Resolving package versions...
  Updating `~/.julia/environments/v1.0/Project.toml`
  [336ed68f] ↑ CSV v0.3.1 ⚲ ⇒ v0.4.1 ⚲
  [d9d29d28] + SingularSpectrumAnalysis v0.0.0 [`~/.julia/dev/SingularSpectrumAnalysis`]
  Updating `~/.julia/environments/v1.0/Manifest.toml`
  [336ed68f] ↑ CSV v0.3.1 ⚲ ⇒ v0.4.1 ⚲
  [7d512f48] - InternedStrings v0.7.0
  [69de0a69] + Parsers v0.2.7
  [d9d29d28] + SingularSpectrumAnalysis v0.0.0 [`~/.julia/dev/SingularSpectrumAnalysis`]

(v1.0) pkg> st
    Status `~/.julia/environments/v1.0/Project.toml`
  [6e4b80f9] BenchmarkTools v0.4.1
  [336ed68f] CSV v0.4.1 ⚲
  ...

(v1.0) pkg> add CSV@0.3.1
 Resolving package versions...
  Updating `~/.julia/environments/v1.0/Project.toml`
 [no changes]
  Updating `~/.julia/environments/v1.0/Manifest.toml`
 [no changes]

Is it expected?