The schema only allows "letter" to be set to "a" or "b", but doesn't catch the value of "c" on the second object in the array. Setting the value of "letter" of the first object to "c" does result in a validation error, as expected.
Your JSON Schema is using tuple typing, so only the first item in the array will be validated. I have corrected your example here: http://pastebin.com/QegcbQGq
Using JSV through vickeryj's validator_form.html, I have a problem with the following JSON schema and JSON:
JSON schema: http://pastebin.com/3f7H6yDT
JSON: http://pastebin.com/rPhR7rym
The schema only allows "letter" to be set to "a" or "b", but doesn't catch the value of "c" on the second object in the array. Setting the value of "letter" of the first object to "c" does result in a validation error, as expected.