Are there examples of significant enhancements to major programming languages that were fully released and then found to be sufficiently flawed that they had to be withdrawn?
UPD @Jeff Foster has an example of a feature that is not consistently implemented and I'd take those as answers
UPD There is a grey area between Deprecated and withdrawn. I suspect that there are thousands of Deprecated examples - which can still be used but are not advised. I can conceive that there are features which some creators thought they could implement fully or consistently but actually broke the integrity of the system.
I was particularly looking for enhancements (not original features) as these will have been planned (probably with community involvement) and released after testing, etc.