Android flag is true on a windowsphone

[leolux]

window.navigator.userAgent of the browser is:
Mozilla/5.0 (Mobile; Windows Phone 8.1; Android 4.0; ARM; Trident/7.0; Touch; rv:11.0; IEMobile/11.0; Microsoft; Lumia 640 LTE) like iPhone OS 7_0_3 Mac OS X AppleWebKit/537 (KHTML, like Gecko) Mobile Safari/537

I would expect the flags "mobile" and "windowsphone" to be true because it is a windowsphone (Lumia 640 LTE)

But detected flags are as follows:
mobile: true
windows: undefined
windowsphone: true
android: true
ios: undefined
blackberry: undefined
firefoxos: undefined
tizen: undefined

Why is bowser.android = true?