With ipython 5.1.0/prompt-toolkit 1.0.9 using the vi keybindings, Esc-/ initiates a forward search. What exactly is the use case for that, and in what situation would such a search find anything? This is not the readline behavior, and therefore this is completely unlike the behavior in bash, prior versions of ipython, or pretty much any other REPL anyone would have used.
I actually thought the search was broken until I discovered that Esc-? initiates a backward search, which is what I really want. It just happens to be that's a more awkward keystroke and it's going against many years of habit.
I can't imagine other people don't find this super frustrating as well, so I'm surprised I didn't find mention of this in any other issue. Unless there's a really compelling case for the current behavior, I suggest that it be reverted.
At the very least, I would like to know if there's a way to rebind the key strokes locally so I can fix this at least on my present installation.