A big thanks to Thom C for digging up the info on how to turn off auto resume when playing back movies after my helpful 3 year old decided to play with the Webpad and turn on auto resume. Below are the instructions and I will have a go at creating a wiki on it
There is no direct UI to re-set this feature, however, you can send a DCE command to the media plugin to set it.
The relevant command is Set Auto Resume Options, and can be found by selecting the Media PlugIn in Advanced > Configuration > devices, and selecting the media plugin, and clicking Send Command.
The parameters are well defined enough so you can figure out how you wish to set it.
Further info - when setting the three strings
# 5 Value To Assign (string)
Valid values are: NEVER, ALWAYS, PROMPT - enter PROMPT to re enable the option of resuming where you left off
# 17 PK_Users (int) - enter your user number ie 1, 2 or 3 etc
# 29 PK_MediaType (int) - enter 5 as the media type