Why is TKinter OptionMenu changing the size of it's parent?

I have this GUI program, and one of the Frames has an OptionMenu in it. Whenever I select something in the OptionMenu, it resizes the parent frame, even though it has more than enough room to fit in the current panel. It's hard to describe in words, so here's an image of what I mean:

You can see that the purple, blue, and red frames have expanded with the size increase of the OptionMenu.

The window is split into two Frames, the left and right, with a Grid Layout, with a weight of 3 and 2, respectively. Inside of the two frames is a Pack layout of each colored panel, set to fill X. Inside of Purple, I have set this optionMenu, and packed it to the left of the panel.

When it changes its contents, it resizes the entire right frame, ignoring the grid weights and throwing off the balance of the GUI. If I set a fixed width for the OptionMenu, it doesn't resize, but still grows the frame out of alignment with the GridLayout. How can I get the frames to not resize based off of the width of this one element, and just place the element inside of the frame, which has more than enough room to handle it, even at it's widest?

Here's a boiled-down version of the GUI code I'm using, the full code is a bit too long since each panel is broken into classes for future functionality:

root = Tk()
root.geometry('640x480')

#Begin defining left frame areas
leftFrame = Frame(root)

grayPanel = Frame(leftFrame,bg="gray")
whitePanel = Frame(leftFrame,bg="white", height=50)
grayPanel.pack(expand=True,fill=BOTH)
whitePanel.pack(fill=X)

#Begin defining right frame areas
rightFrame = Frame(root)

purplePanel = Frame(rightFrame,bg="purple", height=50)
bluePanel = Frame(rightFrame,bg="blue")
redPanel = Frame(rightFrame,bg="red", height=100)

purplePanel.pack(fill=X)
bluePanel.pack(expand=True,fill=BOTH)
redPanel.pack(fill=X)

#create the options dropdown for purple
currentOption = StringVar(purplePanel)
currentOption.set("None")
optList = ["None","Some incredibly long string that breaks everything"]
options = OptionMenu(purplePanel,currentOption,*optList)
options.pack(side=LEFT)


leftFrame.grid(row=0,column=0,sticky=N+S+E+W)
rightFrame.grid(row=0,column=1,sticky=N+S+E+W)

root.grid_rowconfigure(0, weight=1)
root.grid_columnconfigure(0, weight=3)
root.grid_columnconfigure(1, weight=2)

root.mainloop()