The Valueset-ucum-common contains an invalid expression {kp_C}

Validating that at https://ucum.nlm.nih.gov/ucum-lhc/demo.html results in the following response

Sorry - an error occurred while trying to validate {kp_C}
FYI - annotations (text in curly braces {}) are ignored, except that an annotation without a leading symbol implies the default unit 1 (the unity).

Unknown macro: {kp_C}

is not a valid unit expression, but [kp_C] is. Did you mean [kp_C] (homeopathic potency of centesimal korsakovian series)?