When I use SPI.h my digital inputs are broken

Using Arduino Programming Questions
1

Has anyone seen this behavior before? I have an Arduino Leonardo and a push button switch on DIGITAL 6. Works fine.

However, as soon as I include <SPI.h> and <MFRC522.h> (for my RFID reader), the push button stops working. The RFID reader works, but the button cannot be read anymore (I've tried other ports as well).

I'm pulling my hair out... what am I missing?

2

Code and circuit please.

3

if (!mfrc522.PICC_IsNewCardPresent()) return;

Yeah right.... "return".... so the rest of the code is not executed anymore... sorry guys, case closed!

4 
if (!mfrc522.PICC_IsNewCardPresent())
  {
     return;
  }

might have made the problem more obvious.