Transact SQL :: CASE Order Of Evaluation

I have the following query in a user-defined function. It accepts a single string parameter, but for the sake of simplicity, I have substituted actual strings in the query. It basically checks the passed string. If it ends with "Id", it strips off the "Id" and returns the resulting string. If it ends with "Id" followed by a digit, it strips that off and returns the string.

SELECT CASE
WHEN LEN('IncidentViolationId') > 2 AND RIGHT('IncidentViolationId', 2) = 'Id' THEN LEFT('IncidentViolationId', LEN('IncidentViolationId') - 2)
WHEN PATINDEX('%Id[0-9]', 'IncidentViolationId') > 1 THEN LEFT('IncidentViolationId', PATINDEX('%Id[0-9]', 'IncidentViolationId') - 1)
ELSE 'IncidentViolationId' END

This code has worked flawlessly for quite some time and all of a sudden I get "Invalid length parameter passed to left function". I understand why LEFT() would normally fail if I passed it a -1 for the second parameter, but in this scenario, asI understand it, it never should have reached the second WHEN condition since the first one evaluates to true. Why and why all of a sudden?