Api's new 'tools' attribute seems inconsistent with deprecated 'functions' (when expected to call just one function)

I’m testing out replacing the functions deprecated attribute with the new tools one on my existing prompts (with a single function expected) and noticing some inconsistencies with call results (same model, and temperature 0 configuration).

Inconsistencies include hallucinations etc that can probably be solved by adjusting the prompt.
I guess this is kind of expected but still thought it’s interesting as I was kind of hoping for it to behave about the same for straight-forward use cases.

Is there any documentation regarding differences between the two that I’m missing?