Non-deterministic selection of deserializer

[vigoo]

I ran into an issue where something seems to randomly choose from representing an integer field to be deserialized as either config's Value, or serde's Content. When it is the the first, the into_uint logic in Value correctly parses the string configuration (coming from an Environment source) but when it is running into deserializing Content::String then it fails with

Failed to parse config: invalid type: string "1234", expected u16

I could not figure out where the non-determinism is coming from.

The following repository reproduces the problem:
https://github.com/vigoo/rust-config-bug

just running cargo run multiple times, sometimes it works, sometimes fails with the above error.