Home AP will make a second separate network if not set to bridge mode. (I don’t like QuickSet, lack of control)
To add an AP to an existing network, just as an extra AP with no own network range, set everything as bridged (ethernet and WLAN interfaces)
The extra AP will extend the network as a switch, and will just bridge/switch connect the AP SSID (wifi) with the rest of the network (ethernet)
The extra network AP must be connected to the LAN side of the other AP. (Important if that other AP does the transition from WAN to LAN (e.g. Home AP)
Detailed example is here: http://forum.mikrotik.com/t/mikrotik-ap-without-dhcp-integrate-in-existing-subnet/154983/2