foverlaps multiple column check

MWE

library(data.table)

x<-data.table(a=c(1,2),a1=c(1,2),
              b=c(1,2),b1=c(1,2),
              c=c(1,2),c1=c(1,2))

y<-data.table(mina=0,maxa=3,
              minb=0,maxb=3,
              minc=0,maxc=3)

## Does work
setkey(y,mina,maxa)
setkey(x,a,a1)
foverlaps(x,y, which=TRUE)

## Doesn't work
setkey(y,mina,maxa,minb,maxb)
setkey(x,a,a1,b,b1)
foverlaps(x,y, which=TRUE)