Oneway = alternating is what is sometimes called a convoy system. A bunch of vehicles are allowed one way, then another bunch the other way. This might apply over a narrow bridge, or through roadworks. For routing purposes, ignore it being oneway as traffic can flow both ways.
Discussing the OSM tag name is nonsense. The tag is correctly set in OSM and handled incorrectly in Navigator.
Since Navigator cannot handle at which time which direction is allowed, Navigator must handle it like onway = no. Still not 100% correct, but better than now.
there are no times attached to alternative oneway tags, so it does not matter if Navigator can handle it (from memory I think something was done about it some time ago)
but I happen to agree with you, it really is not oneway and should not be treated as such
hopefully it will be corrected in the next map releases