Bird OSPF bug? (Mutliple areas, rfc1583compat off, cost ignored)

I have test lab -- two OSPF routers, Bird 1.6.4: A, B. 2 areas defined: 0.0.0.0, 0.0.0.1. Export "all". When rfc1583compat is Off I observe default route gets propagated via area 0.0.0.1 in despite its interfaces have higher costs than area 0.0.0.0's have. Turning rfc1583compat On changes it to expected behaviour: interfaces costs are respected again. Bug or am I missing some piece of OSPF knowledge here? -- End of message. Next message?