Very good post. I made a similar experience once, but this relates to equipment, not buddy:
After doing the rescue class I thought I was a pretty comfortable diver. Boyancy was spot on and air consumption at a record low. I was completely in control.
Then on one quite deep dive my mask was leaking like crazy. It kept flooding. My boyancy went everywhere, my air consumption went and I had an annoying dive. Turned out there was a relatively big puncture in the silicone of the mask that must have sealed in the early part of the dive, but then let go. No idea how it got there.
I assess myself at how I dive when things do not go according to plan, be it with a less controlled buddy, equipment, environment. This type of diving skill (being still a good diver when things are not optimal) is also the first to go rusty when taking a break from diving (i.e. during a winter period). Although you might dive like always on the first dive of the season, your reaction to problems could be much worse than after a few weeks of diving.
I would like to think that now I would be in control in any circumstance, but I am sure that depends on the circumstance.
Do most divers know what "type" of diver they are when things do not go right? I am sure the variability even among highly experienced divers would be surprisingly large. Some probably remain very calm indeed, but some may end up looking novice?
