facet names incorrectly set may lead to error
task names ( names(x$matlist) ) had been used for facet titles instead of algorithm names ( stored in "ordering").
besides wrong content, could lead to error
Error in names(pl) <- names(x$matlist) : 'names' attribute  must be the same length as the vector 
error has arisen if number of algorithms was smaller than number of tasks, i.e. if length(ordering)=length(names(pl)) < length(names(x$matlist))