Shiny and rCharts/Polycharts with both X- and Y-axis choice input - r

Question

I have a problem where I import a large data set, then generate some selection input from that data set, and then want to be able to have a plot where I can freely choose my x- and y-axis from the data set.
I keep crashing the browser, with my current code - I believe it has something todo with rCharts trying to generate the polychart, with variables not yet available - my custom input has to load first. I've tried both using reactive parts and isolating the output, and other stuff - either I am not doing it correctly, or its not the right way - either way it isn't working.
I am rather new to shiny, R and especially rCharts, but I got my graphs working with only one input - Problem arises when trying to make the multiple selectable.
I have the three following UIs that gives input to the renderCharts, which I show below:
output$TestSelection <- renderUI({
selectInput("TestSel", "Test Variable", ls(df, pattern = ".*?_meas|.*?_calc"))
})
output$customx <- renderUI({
selectInput("xcustom", "Custom Graph - X", ls(df), selected = input$TestSel)
})
output$customy <- renderUI({
selectInput("ycustom", "Custom Graph - Y", ls(df), selected = input$TestSel)
})
And the renderChart2 code:
output$customplot <- renderChart2({
if(is.null(input$xcustom)|is.null(input$ycustom))
return(rCharts$new())
#Removing all unneccessary data from dataframe,
dataPlot <- df[,c("DUT", input$ycustom, input$xcustom)]
custom_chart <- rPlot(x = input$xcustom,y = input$ycustom,
data = dataPlot,
type = "point",
tooltip = "#!function(item){return item.DUT}!#",
sample = FALSE)
#Adjusting width to fit the current screen
custom_chart$set(width = session$clientData$output_plot2_width , title = paste(input$ycustom, " vs. ", input$ycustom, sep =""))
#Setting the correct axis
axisincrease = abs((max(dataPlot[,input$xcustom])-min(dataPlot[,input$xcustom]))*0.05)
custom_chart$guides(
x = list(
min = pretty(dataPlot[,input$xcustom])[1]-axisincrease,
max = tail(pretty(dataPlot[,input$xcustom]),1)+axisincrease,
numticks = length(dataPlot[,input$xcustom])
),
y = list(
min = pretty( dataPlot[, input$ycustom] ) [1],
max = tail( pretty( dataPlot[, input$ycustom] ), 1 )
)
)
return(custom_chart)})