For me, there is no pattern that I could see and I have been working with this since I got the unite. To the point, my HD500 was replaced.
Here are some things I have noticed that may or may not have anything to do with it. I have a patch that has foot switch 1,2,3,and 4 that turns off and on effects. With the HD500 connected to the editor, I turn off any one of the foot switches. Close the editor, and turn off the HD500. When I turn the HD500 back on, the foot switch I turned off is still off. It should have gone back to it's normal setting with the foot switch on. If you change a patch in any way (not connected to a computer). With foot switches or any other change. Then switch to another patch then go back to that patch. It reverts to it's original state.
that above here is a normal behaviour..
when you load any patch you are using and eventually editing only a copy of that patch in a special temporary memory buffer..
the original memory slot is preserved, and changed only if you specifically save the patch into that slot..
every time you turn on your POD it works automatically with the edit buffer memory and the settings that were and are still in there.. that buffer memory automatically memorizes every last action you did with your POD: on/off state, knob settings etc.. from when you loaded the last patch..
the only way to change the edit buffer memory is to load another patch (or even the same patch number again), or doing some editings
so, in few word you are always using the edit buffer memory and not the original saved data, even if you are still seeing the memory slot bank number/patch letter from where the data came from..
Also, open the editor with no HD500 connected. A message window opens, telling you there is no HD500 connected and the editor will run off line. Make a patch with two amp and as many effects as possible (exceed the DSP). Save it to your desk top (it will save it). Then connect your HD500 to the computer and open the editor. Drag the patch you made into the editor that the HD500 is not set to. Meaning, drag it to 4A, and the HD500 is on 3A. It will load, and work at first. I did this, used the patch all day. Came back the next day and it would let me use it, because the DSP was too much. Like I said, may or may not have anything to do with anything. The point is, this kind of stuff should not happen. You do the math.
for the other issue above, I believe that the edit program when in off-line mode doesn't sense the hardware limits of the POD, and for that reason it lets you do patches more DSP expensive than normally possible for the HD..
even if you can send them temporarily in your POD, I don't believe that they'll be full working..
anyway this discrepancy is something that needs to be fixed..