Horizon Hobby have identified a possible problem with the stick potentiometers in some Spektrum DX6i transmitters. The symptom is jerky response to moving the control sticks. In particular sets with date codes (found inside the battery cover) of 809E, 810E, 811E, 812E may be affected. However if the date code has "UK" after it, then this set has been tested by the UK distributor and found to be OK. Instructions for checking this are on the Horizon Hobby site.

(thanks to Don Brazier for drawing attention to this).