Legacy GM (RESOLVED) sprite_index resets itself to -1

I just came across another issue today.
for some reason my projectile objects are resetting themselves to -1 in between the Debug alarm[0] event and the Projectile step event.

I followed the debugger to these points and I can't find out what is causing it.
I am using a variety of code so I thought it would be best to upload my project and link it here.

https://drive.google.com/open?id=0B16wNFPwi_2kb0xwLTZRMlRBMjg

it might be a bug and if so I need to verify it so I can report it.
 
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