Using -a ADAPTER... is alternative syntax for specifying a 5' adapter and is currently equivalent to -g ^ADAPTER. The -a option should not do implicit anchoring and instead it should be equivalent to -g ADAPTER. Since this feature is underdocumented (if at all), backwards compatibility is likely not an issue.
However, in addition the same should apply for linked adapters. -a ADAPTER1...ADAPTER2 currently automatically anchores the first adapter, but it should not do this. This is backwards incompatible.