Airport Express configuration failure on Yosemite

On Yosemite 10.10, the first time set up of my Airport Express A1264 through Airport Utility fails if both the Ethernet and WiFi are enabled (meaning my Mac has two IP addresses).

The first time set up of my Airport Express A1264 through Airport Utility succeeds if the Ethernet is disabled and only the WiFi is enabled (meaning my Mac has only 1 IP addresse).

Is this a Yosemite bug?