Reporting from my home machine so system information here isn't useful unfortunately, sorry. I can paste information from the Windows box I experienced this on tomorrow.
To reproduce: On a Windows version of Emacs:
Evaluate (parse-time-string "2018-03-05")
A list of all nils is returned.
Removing the lexical-binding from parse-time.el solves the problem. lexical-binding seems to have no effect on Linux.