I2C action is limited to the SCL and SDA pins you have defined (you haven't said what version of compiler you've got - just in case it's some ancient issue from years ago). The 16F628 has analog comparators which in certain modes can cross-connect some pins (see schematics in Comparator Section in Datasheet), but if you have disabled Comparators and the Voltage Reference Module this won't happen and it certainly won't happen with PortA.7 whose only commonality is with the Oscillator circuitry. You may have some bum code, or more likely a short between pins on your PCB or Breadboard since RA7 (your problem pin) and RA0 (your I2C pin) are adjacent.