I have noticed this issue as well, and upon starting the installer removed the usb device and procceded with the install as normal. when i got to the bootloader and started installing it i quickly switched over to tty4 and noticed that during the install its forcing it to be installed at /dev/sda which in my case the internal hard disk is ignored even if selected as the option to install it. for me it was sdb.
there is a very unwarrented behaviour