First ping sensor in array not working

I am using the 15_Sensors_Example (https://code.google.com/p/arduino-new-ping/wiki/15_Sensors_Example) from NewPing library by @teckel and slightly modified it for 12 sensors. I have the sensors hooked up to a mega + Yun Shield. The first sensor always reports a 0, or rather "no ping".

The way i fixed it temporarily is I added a fake sensor to the beginning of the object array and when i go to upload the data, I just ignore that first sensor.

However, I would like to figure out what could be causing this. Power? Timing?

Also, the issue does not happen when i remove the Yun Shield and just have the Mega 2560 print to Serial.

Any paths i could take? Any potential things i could test?

What is the first sensor's trigger pin#, echo pin#?

It does not matter, I have tried it on multiple pins none of them worked. The only thing I've got going on is that the trigger and echo are on the same pin, but the HC-SR04 is capable of handling this.

How do you power it? from USB or DC Adapter?
The cable length of first sensor?

If you are moving the hardware around and experiencing the same problems, then it's likely to be something in the software. Please post your complete current code, it's likely we may see something you're missing.