'05 GC A/C issues

I have a strange issue with my air condition on my '05 Grand Cherokee Limited 4.7L. My brother had borrowed it on a 600 mile road trip and on his way home today, he got stuck in traffic. He called me at that point and told me that the A/C seemed to have quit working. When he got home I hooked up my gauges and notice it was slightly low on freon. I added about 9 ounces of freon and the air was back to blowing cold again and the gauges were reading normal for the ambient temperature outside.

He is what baffles me. Before I did anything, I started the Jeep and turned both climate controls (it has dual-zone) as cold as they would go and put the fan on full blast. I looked under the hood and the compressor was on constantly and the electric fan turned on. However, the air coming out of the vents was hot.

What I don't understand is it only needed about 9 ounces for the air to run normally again and for the gauges to read normal as well. So why wasn't the compressor cycling signalling a low charge? With all the A/C's I have worked on, when a vehicle is low on freon, the compressor cycles. So why wasn't my compressor cycling? The system holds around 1.5 pounds of freon. I would assume that the system being around 9 ounces low wouldn't cause the vents to blow hot air, especially when the compressor is running constantly and the electric fan has turned on.

I assume I have a small leak somewhere. But is it normal for the compressor to constantly run even with a low charge on these newer jeeps? Any input would be greatly appreciated it. Thanks!