Troubleshooting (pun intended)

[wippit]

Hello all! Took my USED Zastava ez9 to the range yesterday and I'm having an issue. After the gun cycles it only goes into SA mode about half the time. As in the hammer is not cocked even though it cycled properly. I can continue firing in double action fine. If I mag dump I randomly get half DA and half SA shots. I noticed while I was playing around with it if I keep the trigger completely depressed and try to manually cock the hammer, the hammer will not catch. I have to let the trigger forward ever so slightly before the hammer will stay cocked. This is my first semi-auto handgun, but I'm pretty sure this isn't right. I'm pretty sure it's a sear issue but any help would be appreciated.
SIDE NOTE: I don't need a lecture on my choice of purchase, I have plenty of reliable handguns and this is not a carry gun.

[wippit]

http://i.4cdn.org/k/1429464474369.jpg
This is what it looks like with the trigger depressed. The sear is isn't even close to the trigger catch, I had someone tell me that this is normal but that can't be right.