Loosing Safari Drop Down Box

I have a line of code that opens a dropbox with months and current month selected what I want to do is select the next month. I can access the box either by clicking at its location or by code instruction.
unfortunately when I try to access the next month the opened box closes.

tell application "System Events" to tell process "Safari"

	click pop up button 1 of group 1 of group 1 of group 13 of UI element 1 of scroll area 1 of group 1 of group 1 of tab group 1 of splitter group 1 of window 1
end tell