Mysterious problem changing channels w/ USB-UIRT & QIP7100

[enyin]

Hi all,
I've recently starting having mysterious issues with my channel changing -- my setup has been stable for years, and i haven't made any major changes to the setup in almost 2 years. The problem just started occurring with no other changes made in the system.

I'm using HD-PVR w/ USB-UIRT to tune a Fios QIP7100.

When the system tries to tune a channel, about 25% of the time now its skipping some of the numbers. So for example if i try to tune channel 509 sometimes i get 0009 or other combinations. This is happening on any channel. I can see the USB-UIRT flashing on the change and it gets the right channel about 75% of the time. After it messes up, if i immediately try to go back to the right channel, it usually works.
I've made sure the sensor is properly positioned (same as it has been for years).

I'm not sure where to start since its been working fine for years and i haven't changed anything. I tried tweaking the delay settings, right now its at:
infrared_receive_repeat_delay=250
infrared_receive_repeat_delay_rc5=350
infrared_receive_repeat_period=150

Any suggestions on what to check?