Hierarchy Constraint Violation -- salesforce.com

Salesforce has thrown a new error message at me, and so far I haven't found anything useful in the docs about this. I am trying to save an object in a controller extension, and it does in fact save th开发者_运维技巧e record, but instead of returning to the page that I indicate, it shows me the error message "Hierarchy Constraint Violation". In looking over the debug logs, this does not show up anywhere, despite the fact that I log as error any DML exceptions and re-throw them. I am not stifling any other exceptions, either.

I can't tell what this error even means, let alone where it is coming from.

The problem turns out to be an attempt to create a self reference.