Hi i just came across the same problem when i connected a new wifi dongle into my new rpi b+. It must be some sort of emi which i need to investigate further. Try using a shield between your ir receiver and your wifi dongle, or just use lan. Which is what im doing for now. This is what lirc say about it:
Checking module based receivers
NOTE: This section only applies if your device requires a lirc_[driver] kernel module.
Before you start using lirc, you should check if your receiver is working, and if there is IR interference. Possible sources of interference include monitors/televisions (especially plasma displays), fluorescent lamps and direct or ambient sunlight. Start the following command to display raw receiver input.
# mode2 -d /dev/lirc0
If you press buttons on any IR remote, you should see a series of pulses and spaces. If there is very frequent output without pressing buttons on your remote, your receiver suffers from interference. You want to avoid such interference, e.g. by placing the receiver behind or under your plasma tv.
If you can't make out where the interference is coming from, you can try to put a cardboard roll right in front of the receiving diode, so that it only gets light from a specific direction. Invoke mode2 as above. Then point at different locations till you receive IR noise.
Here's is another good article on disturbance
http://www.vishay.com/docs/80072/disturan.pdfLet me know how you get on