why does ifup wlan0 also configure wlan1?

This is really strange. I'm using a raspberry Pi 3 which has builtin broadcom wireless. Works great. I added a Realtek usb wirless adapter because it has an sma connector. Installed firmware. Works great.... when the interface will come up that is.

Sometimes when I boot the Pi 3, wlan0 (realtek) will not get an IP address from dhcp. Sometimes it will. If I type ifdown wlan0/ifup wlan0 (brroadcom) wlan1 will also sometimes get an IP address.

Now this is really telling: If I bring down both wlan0 and wlan1 then type ifup wlan1 (realtek), wlan1 does not come up but wlan0 does!!!

I've always wondered how does linux knows that wlan0 is the built-in broadcom wireless while wlan1 is the Realtek wireless because I got this error in dmesg:

[    5.834507] brcmfmac: brcmf_add_if: ERROR: netdev:wlan0 already exists 

/etc/network/interfaces:

auto lo iface lo inet loopback  allow hotplug eth0 iface eth0 inet dhcp  allow-hotplug wlan0 iface wlan0 inet manual     wpa-conf /etc/wpa_supplicant/wpa_supplicant_wlan0.conf  allow-hotplug wlan1 iface wlan1 inet manual 

/etc/wpa_supplicant/wpa_supplicant_wlan0.conf (_wlan1 is identical):

country=CA ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev update_config=1  network={         ssid="nexasdevnet"         psk="workingatnexasisfun"         key_mgmt=WPA-PSK } 

/etc/dhcpcd.conf has not been modified

Output from lsusb:

Bus 001 Device 006: ID 0403:6010 Future Technology Devices International, Ltd FT2232C Dual USB-UART/FIFO IC Bus 001 Device 005: ID 0bda:8178 Realtek Semiconductor Corp. RTL8192CU 802.11n WLAN Adapter Bus 001 Device 004: ID 046d:c31c Logitech, Inc. Keyboard K120 for Business Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub 

Relevant output from dmesg|grep usb:

[    3.109820] usb 1-1.3: new high-speed USB device number 5 using dwc_otg [    3.211164] usb 1-1.3: New USB device found, idVendor=0bda, idProduct=8178 [    3.213327] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [    3.215399] usb 1-1.3: Product: 802.11n WLAN Adapter [    3.217397] usb 1-1.3: Manufacturer: Realtek [    3.219375] usb 1-1.3: SerialNumber: 00e04c000001 

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Category: linux Time: 2016-07-29 Views: 0

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