bcmwl's wl module fails to load: unknown symbol on Bionic

On a Bionic Beaver system I installed via debootstrap (I used debootstrap as a separate issue in Ubiquity prevented me from installing it the old fashion way. Namely Ubiquity froze at the step of choosing whether to download updates during installation, and whether to install third-party, potentially proprietary software for WiFi cards, codecs, etc. But serves me right from expecting things to work well in a developmental release) I installed bcmwl-kernel-source. The installation went largely well, except it seemed to be experiencing a problem with loading the module. modprobe -a wl returns:

modprobe: ERROR: could not insert 'wl': Unknown symbol in module, or unknown parameter (see dmesg)

the lines in dmesg relating to wl are:

[ 10.892819] wl: loading out-of-tree module taints kernel.
[ 10.892822] wl: module license 'MIXED/Proprietary' taints kernel.
[ 10.892823] Disabling lock debugging due to kernel taint
[ 10.894423] wl: module verification failed: signature and/or required key missing - tainting kernel
[ 10.894455] wl: Unknown symbol cfg80211_inform_bss_frame_data (err 0)
[ 10.894470] wl: Unknown symbol cfg80211_scan_done (err 0)
[ 10.894488] wl: Unknown symbol cfg80211_disconnected (err 0)
[ 10.894506] wl: Unknown symbol wiphy_new_nm (err 0)
[ 10.894510] wl: Unknown symbol wiphy_register (err 0)
[ 10.894513] wl: Unknown symbol cfg80211_put_bss (err 0)
[ 10.894514] wl: Unknown symbol cfg80211_roamed (err 0)
[ 10.894517] wl: Unknown symbol cfg80211_gtk_rekey_notify (err 0)
[ 10.894521] wl: Unknown symbol cfg80211_ibss_joined (err 0)
[ 10.894526] wl: Unknown symbol cfg80211_michael_mic_failure (err 0)
[ 10.894529] wl: Unknown symbol ieee80211_get_channel (err 0)
[ 10.894533] wl: Unknown symbol wiphy_unregister (err 0)
[ 10.894537] wl: Unknown symbol cfg80211_get_bss (err 0)
[ 10.894549] wl: Unknown symbol ieee80211_channel_to_frequency (err 0)
[ 10.894553] wl: Unknown symbol cfg80211_report_wowlan_wakeup (err 0)
[ 10.894557] wl: Unknown symbol cfg80211_inform_bss_data (err 0)
[ 10.894559] wl: Unknown symbol ieee80211_frequency_to_channel (err 0)
[ 10.894563] wl: Unknown symbol cfg80211_connect_done (err 0)
[ 10.894565] wl: Unknown symbol wiphy_free (err 0)

I have tried rebooting after I get this error, just in case the kernel merely needed to be reloaded (doubted it would help but still worth a try), but alas that didn't help. If relevant I am using a Btrfs file system (why? Because of snapshotting of course, I am using a developmental release after all).

All the commands I have executed in it since the beginning of time (which was only a few hours ago, at most, so there isn't much to it) can be found here in its root bash_history file:

https://gist.github.com/22fdcbead4ce240230fa09f92a730a90

So is this something I should report as a bug or?