Explanation:

This bug is documented at Gamefaqs.com in the Super Metroid Glitch FAQ.  It is known there as met.exploit.reset and met.spazplas.

Anyone who has played Metroid 3 enough can tell you that you can't equip Spazer and Plasma together.  I can tell you they are wrong.

Sorry to anyone I might have offended by using this glitch - I know it isn't mine and want to give full credit to Brickroad for making the FAQ where I found it and michaelangelo for discovering it.