No disconnector function w/the safety out?
Something's wrong; either w/the part(s) or with the installation. First place I'd look is the disconnector spring. Make sure it's 1) there and 2) installed the right way.
The safety on a semi auto only AR15 has abolutely no relationship to the trigger/disconnector function; except to impose a block that prevents those parts from moving when it's engaged.
Whatever the problem turns out to be, you're in no danger of full auto fire in any event. If the disconnector on a semi auto gun is removed, fails, or doesn't function, all that happens is that the hammer wil follow the second round feed down and come to rest on the primer of an unfired round.
Why am I so sure of this? Because as an experiment we took the full auto sear and disconnector out of my class three'd Colt one day, and tried to make it fire more than once w/three different brands of 5.56 ammo. Same result every time. One fired, and the next one ended up unfired w/the hammer down-----just like Gene Stoner and crew intended