SSD
I should perhaps add a bit to my first response, which was:
By "Stall" in this case I meant the maximum ift we could use. There was in fact a small 'hiccup' in the lift curve against AoA, but the lift went up again afterwards. However, there was a definite nose-up 'break' in the pitching moment which we took to be the limiting AoA and regarded as a 'stall'
Although delta wings do not stall in the classic sense there is nevertheless a limit to what lift they can provide. As the AoA increases the vortices also increase in intensity, but there comes a point where the vortex flow becomes unstable and the vortex 'bursts', i.e. the circular motion degenerates into chaos and the diameter of the 'vortex' increases greatly.
The point in the vortex track at which this happens moves up towards the wing TE as AoA increases and when it reaches the TE the wing pressure distributions change and you get a break in the pitching moment curve. This happens earlier on one wing if you have sideslip, so you then tend to get a wing drop. This does not meet the airworthiness requirements so effectively vortex bursting over the wing equates to stalling.
[On another thread it has been pointed out that on the FA18 vortex bursting (off the LE extension) has caused handling problems due to interference with the fins]