Okay, I played around with this today (although "play" is probably not the correct word 🙄 ), and I think I have some insights.
I created a small Flash-DisplayList demo application; the source can be found here. Use this class as Startup-class for a pure Flash project, or instantiate it from such a startup class.
Just like my previous Starling example, it draws a point to the screen each time a touch occurs. (That way, we're not getting sidetracked by delays in the trace-output.)
Note that the "onEnterFrame" method does some time-consuming nonsense, and you can modify the "count" constant to make it more expensive.
With that prepared, I noticed the following:
Whenever the AIR app does not succeed in providing the FPS that you requested, Touch and Mouse (!) events will queue up.
You can reproduce this like this:
1) Set the requested frame rate to 30 (via
[Swf(frameRate="30")] on top of your startup class).
2) Find a value of "count" that makes Flash sufficiently busy so that it doesn't reach those 30 fps and stays at about, say, 25 fps.
3) Now touch the screen with 5 fingers repeatedly, or click really fast with the mouse.
→ The touch events will queue up. If you enable the Windows feature that shows touch events on the screen, you'll see that even those visualizations become delayed.
4) Now change "count" so that the 30 fps are actually delivered.
→ Touch and mouse events will no longer queue up.
This means that you can avoid that the touch events queue up by selecting a "frameRate" that Flash can actually deliver!
5) To prove this, set the "count" value back to the value that delivered 25 fps.
6) Set the "frameRate" to 20.
→ Touch events will no longer queue up.
I could recreate the same outcome with a Starling project, as well.
@stortof, you said that you created an app for a museum, so you're probably working with specific hardware (that's always equally fast). Thus, if you set the frameRate to a suitable value once, the problem should go away on all those devices. (Or, alternatively, optimize your code that the target frameRate is always easily reached.)