Yes, in my opinion, it is the normal behavior of the Amazon Music app. By default, it will be played on devices that have the Amazon Music app installed, and it will be optional to play on WiiM devices with AlexaCast.
But as
@Brantome said, the current Amazon Music app can stay connected to WiiM for a long time once connected to WiiM with Alexacast.
As shown in this image, the glowing blue cast icon in the Amazon Music app indicates that you are connected to your WiiM with Alexacast. What happens if you close the app in this state and then restart it? Normally, when you open the app the next day, the icon will still be glowing blue, and you're still connected to the WiiM, so you can simply press the play button to play music from the WiiM.
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