> I'd like to keep the active buffer visible while capturing.
That's how it works for me. I do not see a calendar buffer unless I do something like C-c C-d (org-deadline) or C-c C-s (org-schedule) in an org buffer.
If I am in a frame with one buffer ABC, calling org-capture splits the frame into 2 windows: one with ABC and another with Capture.
If I am in a frame already with 2 windows and if my point is in buffer ABC, calling org-capture will retain the ABC buffer (where my point was) and open Capture buffer in the other window.
I do not have display-buffer-alist customized for Capture buffers.
Can you reproduce the problem you see in an emacs -Q session? If so, can you provide a recipe to recreate that over here?
Can you also post your emacs and org-mode versions?
Here are mine:
Emacs version: GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.23)
of 2016-01-12, built using commit 0ed0a9b7f09495394dc9b60a9f7c937679c49afe.