SPI.h library

Hey, folks!
I have veeeeery strange issue here:
yesterday sketch compiles just fine, runs just fine - SPI.h and SPI.cpp are in the same folder as sketch is, is included like this : #include "SPI.h"
Today it runs fine until only god knows why it jus does not compile and throws out error, that SPI is defined two times (one in sketch folder, one in arduino/hardware...etc). And now only way to run all the sketches (and compile them) is to redefine to #include <SPI.h> and delete SPI.h and SPI.cpp files from sketch folders.
What the hell did just happened to me?
SPI.h and SPI.cpp was open from one sketch folder in a text editor (because I was using it as a reference to write my own library) but I didn't do anything.
Any ideas?

SPI.h and SPI.cpp are in the same folder as sketch is

That is NOT where the SPI library belongs.

Today it runs fine until only god knows why it jus does not compile

If the code won't even compile, there is no way in hell that it "runs fine".

It ran and compile fine until one moment when it didn't. That's the strangest part.

Long time prior yesterday #include <SPI.h> was giving errors that the compiler can't find it or something like that (can't remember because it was long time ago), then I've moved it to Arduino custom library folder, until I have started working on a project, that it needed all libraries in one folder (because of sharing reasons), then this happened.
I know that now it works as a standart Arduino IDE should, but for me it is kind of confusing, maybe some day this will happen again.