can only register one IR signal every two seconds

I've just discovered that on my server, the USB-UIRT seems to receive only about one code every two seconds.
Here's the story.
Let's say I'm repeatedly pressing a button on my remote. On one of my USB-UIRTs, this works -- I see the USB-UIRT repeatedly flash its red light and Girder registers each event.
On the other unit, I see one flash of the red light (signaling the first reception), Girder fires its event, and then nothing happens for about two seconds (even though I am repeatedly pressing the button on the remote)... and then after about two seconds, the light flashes and Girder fires the event again.
The two machines in question have very similar GML files, but there may be a critical difference that I don't know about.
I can't find any configuration option that would be causing this.
Here's the story.
Let's say I'm repeatedly pressing a button on my remote. On one of my USB-UIRTs, this works -- I see the USB-UIRT repeatedly flash its red light and Girder registers each event.
On the other unit, I see one flash of the red light (signaling the first reception), Girder fires its event, and then nothing happens for about two seconds (even though I am repeatedly pressing the button on the remote)... and then after about two seconds, the light flashes and Girder fires the event again.
The two machines in question have very similar GML files, but there may be a critical difference that I don't know about.
I can't find any configuration option that would be causing this.