This was the culprit 
Delete the
save plot.png
- it is wrong, it requires quotes on the name otherwise gnuplot it treats the plot and png as variables and the dot . as the concatenation operation.
- the global commands are executed before any plot. Setting a filename has no influence if you dont redirect the output of gnuplot to a file. Let flair do the saving automatically when requested
In my settings I have the
set format "%h"
which forces the axis to use a human number formatting (look the gnuplot manual). Otherwise on log plots you might get some very weird numbers
