An argument that repeats its parameter's default value may be left out,
but the value was only ever compared against the method the call
instruction names - for a virtual call the base declaration, since that
is the slot the compiler emits. The shortened form binds against the
receiver's static type, where an override is free to declare a different
default, and the recompiled code then passes that one instead. Calls have
had this since optional arguments were introduced; opening indexer
accesses to omission brought it to element accesses too.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Siegfried Pammer