I got a really strange behaviour with my esp8266 (on NodeMCU 1.0).
I uploaded this code on my device (via Arduino IDE):
http://pastebin.com/fHn6dHP3
This should only create an access point with the ssid ESPap.
After log in into the network, I could access the HTTP Server on 192.168.4.1. BUT I also could reach the device using 192.168.1.15 (my home wifi). In the past, the esp8266 was already a wifi client of my home wifi.
Why can I access the device on both IP adresses?