80d Manual Focus Single Shot Delay Between Shots

Good morning,

Last night I was shooting some fireworks and noticed what I thought was peculiar behavior of my 80d. In manual focus, bulb mode, f/16, 100 IS0, and single shot mode I noticed about a 1/2 second delay between releasing the shutter and pressing it again for the next shot. Today, I did some experimentation by turning off things like flicker detection and the like to no avail. Long exposure noise reduction was already off. The camera does say "busy" before it triggers the shutter another time. In continuous shot mode, the shutter actuates very quickly up to the 20 raw buffer limit.

Shooting with a Lexar Professional 32 GB 633x card, 24-70 f2.8L lens, using tripod and wired remote shutter release (Canon's).

Any ideas on what the delay could be? If so, is there anything I can do to minimize it?