OK here are some searches, and resulting values:
#battlefornumber10 cameron | timechart span=10m count AS "Total number of Tweets mentioning Cameron"
time cameron
21:10 10325
01:10 144
#battlefornumber10 miliband | timechart span=10m count AS "Total number of Tweets mentioning Miliband"
time miliband
21:10 1759
01:10 96
#battlefornumber10 cameron | timechart span=10m count AS "Total number of Tweets mentioning Cameron"| appendcols [search #battlefornumber10 miliband | timechart span=10m count AS "Total number of Tweets mentioning Miliband" | fields "Total number of Tweets mentioning Miliband" ]
time cameron miliband
21:10 10325 12
01:10 144 1759
So the "cameron" column returns the same number of results, but the "miliband" column has reduced from 1759 to 12 for 21:10
However, looking at a different time 01:10 it appears the values for Miliband have been pushed to the future (+4 hours)
What is happening here?
A better approach would be like this
#battlefornumber10 cameron OR miliband | eval Type="Total number of Tweets mentioning ".if(match(_raw,"cameron"),"Cameron","Miliband")| timechart span=10m count by Type
Run it again without the | fields in your append. The | field means you are not transferring the time field from the timechart, you are just transferring the data field.