Did you make sure that each display has it's own location ?
You will need to adjust the anchor if you want them both displayed at the same time.
If you notice in Fizzle's example code:
Lua Code:
f:SetPoint("CENTER",UIParent,"CENTER",frame_x,frame_y)
If both addons have the same anchor point their information will overlay each other on the screen.
If you notice there is a frame_x and frame_y value there. If you are using the same code for your addon you can have each addon have different frame_x/frame_y values so that the frame will not overlay each other.