Time Machine Backup over WiFi Causes Erratic Magic Trackpad Behavior My Setup
I have a mid-2010 13" MacBook Pro running OSX 10.4.8.
TimeMachine is configured to run hourly backups over WiFi to a TimeCapsule.
I also have a Magic Trackpad linked to my computer via Bluetooth.

The Problem
When TimeMachine begins its backup, if my computer is not connected via ethernet (WiFi connection only), the cursor controlled by the Magic Trackpad moves erratically to the point of being unusable for the duration of the backup.  When the TimeMachine backup completes, normal movement/responsiveness to Magic Trackpad gestures is restored.  

Current Workaround
If I repeat the process but use an ethernet connection, there is no erratic cursor movement.

What I've tried
At first I presumed a hardware issue was to blame, but I tried with my dad's trackpad and got the same behavior.

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Has anyone else experienced this?Is there any workaround besides keeping my laptop connected via ethernet?
Try connecting to 5GHz channel. Rumor has it that the trackpad is sensitive to interference with 2.4GHz wifi.