I used a simple QueueRanked query with multiple elements and a single classification:
QueueTrended(reportsuite.id = "ag-adi-eu-prod",
date.from = "2016-02-01",
date.to = "2016-02-01",
top ="1000",
metrics = c("visits"),
elements = c("evar5"),
classification = "Country (c)",
date.granularity = "week", segment.id = "", data.current = TRUE,
expedite = FALSE, interval.seconds = 5, max.attempts = 10000,
validate = TRUE, enqueueOnly = FALSE)

However using multiple elements:
QueueTrended(reportsuite.id = "ag-adi-eu-prod",
date.from = "2016-02-01",
date.to = "2016-02-01",
top ="1000",
metrics = c("visits"),
elements = c("evar5","mobiledevicetype"),
classification = "Country (c)",
date.granularity = "week", segment.id = "", data.current = TRUE,
expedite = FALSE, interval.seconds = 5, max.attempts = 10000,
validate = TRUE, enqueueOnly = FALSE)

This will result in the following error:
Error in if (!is.null(elements[i, ]$classification) && nchar(elements[i, :
missing value where TRUE/FALSE needed

It seems using classification only works on a single element instead of the first element.