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When interaction terms or offsets were present, ‘drop.terms’ and ‘[.terms’ could return a ‘terms’ object with invalid ‘predvars’ and ‘dataClasses’ attributes. One consequence was that ‘x[-j]’ and ‘x[seq_len(n)[-j]]’ could differ for objects ‘x’ with ‘n’ terms and indices ‘j’ in ‘seq_len(n)’.
The S4 methods for ‘initialize’ with signature ‘.Object="oldClass"’ or ‘.Object=".environment"’ evaluated arguments of type ‘"symbol"’ or ‘"call"’ when dispatching next methods, causing misbehaviour of ‘new(Class, ...)’ with symbols or calls in ‘...’. Thanks to Alexis Sardá-Espinosa for the report (PR#16629).