Here are my thoughts. I am now starting to think you don't have issue with IR level, you likely have an issue with RF interference or possibly a ground loop. Do you have anything plugged into the extender besides the emitter you are testing?
IIRC, these units run around 900MHz which used to conflict in the US with some cordless phones.
Try changing the channel/id on the extender to other values to see if that improves things. Note that you will need to setup your configuration to match the values you choose. I think that you may have to do this for every activity/device that contains IR codes. System properties may not be enough.
