One can find absurd behavior in corner cases of any non-trivial language, but one can find absurd behavior in YAML without even looking for it.
e: And, AFAIK, I believe the latest YAML 1.2 spec (from 2009) has addressed these issues.
Parser implementations have also been buggy. The ruby one in particular being a source of RCE's. Of course, these are implementation issues, but surely a simpler specofication would be easier to implement. And the current specification is anything but simple, clocking 84 pages in the PDF flavour.
It's possible to avoid these pitfalls - like people do with PHP - but why burden users with that in a new project when better options have been available for years?
They obviously like Rust, why not just follow their lead with TOML?
It's a language that coerces basic strings...