Projectile is not ignoring files

Question

I followed the docs here and added lines to .projectile like

-/build
-/Docs/doxy

I did that because I want typical projectile commands to ignore those sub-directories in my project directory.

My "project" is pretty typical. It is a hierarchy of directories with source code files, CMakeLists.txt, and other things. I put this .projectile file in the root folder to mark it as a project for projectile. That part seems to work, because the various projectile commands seem to be using that folder as a project root now.

However, when I run projectile-find-file, and then type part of a filename in the minibuffer, it doesn't just match against source code, it matches object files in the build directory, and .html files generated by doxygen in the Docs/doxy directory. I usually don't want to open these things in emacs, and I'd like it to ignore these files.

Shouldn't it be ignoring them, because I added those lines in the .projectile file?

Maybe I should also mention I enabled IDO with (ido-mode t) so when I'm typing in the minibuffer to find the file it's matching any file in the tree, going into subdirectories. Eg, I type "View.cc", and the displayed list of potential matches looks like:

MyApp/BrowserView.cc     (good)
MyApp/PracticeView.cc
MyLib/UILib/View.cc
build/CMakeFiles/.../BrowserView.cc.o    (bad)
... many more ...