Warframe switches to Scanner and refuses to unequip it.

[UnderRevision]

I encountered this while trying to solo hunt a Teralyst.  In the middle of the fight, my Warframe (Inaros) decided to unequip my Lanka and switch to the Synthesis scanner.  My Lanka was the only weapon I had equipped other than my archgun (Imperator Vandal).  The weapon switch button had no effect.  Selecting the scanner on the gear wheel would make my warframe draw the Lanka but the moment I attempted to fire, it immediately switched back to the scanner without firing a shot.  I could summon my archgun and fire it but the moment I dismissed it the scanner took over again.  Archwing had no effect either although I didn't think to use my K-Drive.  I also tried switching to my tranq rifle but the moment I unequipped it the scanner came right on back.  Transference didn't help, nor did jumping in water.  Even death only let me get off a single shot before the scanner returned.

Needless to say, this made it impossible to kill the Eidolon (archgun might as well have been firing ping-pong balls) and I was forced to abandon the mission.  I've noticed that ever since the melee update the scanner has been iffy when it comes to accepting that I no longer want to use it.  I've have instances where I scan, then switch to a weapon, use melee, then attempt to fire only to discover my scanner has equipped itself.  For now, I'm removing the scanner from my gear wheel entirely.

Unfortunately, I have no idea how to reproduce this bug.  My only suggestion would be to attempt various permutations of switching between the scanner, weapons, and possibly other gear items to see if there are any odd interactions.  I was spamming a lot of healing items because I am bad at the game and that's the only way I can survive a Teralyst, so maybe it was something to do with that.