Custom legend in ggpairs disappears after changing theme

I am having problems with a vanishing legend in ggpairs.

I add a legend inside the top part of a lower triangular ggpairs plot as follows.

First I create a ggpairs plot without legend then I strip the legend I want from and ad hoc graph and place in the ggpairs plot it with putPlot. It works nicely until I try to modify the theme which makes the legend disappear.

# 1 produce graph without legend

plotwithoutlegend <-ggpairs(
    mapping=aes(color = Species,
                shape= Species,

#2 grab the legend from a graph with the legend I want (without alpha).

auxplot <- ggplot(iris, aes(x=Petal.Length, y=Petal.Width, 
                      fill=Species)) + geom_point()
mylegend <- grab_legend(auxplot)

# 3 place the legend in the ggpairs grid with putPlot

graph1 <- putPlot(plotwithoutlegend,mylegend,3,4)

However if I change some aspect of the theme the legend disappears.

graph2 <- graph1 +theme(strip.background =element_blank(), 
                        strip.placement = "outside")

I have asked this question in stackoverflow and got a soluction using the grid package, I just wonder since the problems is with theme, if there is a solution within ggplot2 and ggpairs.

Wow. It fails when just trying to add an empty theme().

show(putPlot(plotwithoutlegend + theme(), mylegend, 3, 4))

show(putPlot(plotwithoutlegend, mylegend, 3, 4))

Reported in Custom legend in ggpairs dissapears after change of theme. · Issue #417 · ggobi/ggally · GitHub

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