I'm assuming you did the second option from my previous post. as I wrote there, that overwrites all the data in the receiving map.
to merge the data - you will need to use the first method ("to copy one object...") too - copy and paste each object separately (there might be a better way but this is what I know how to do). If you have a lot of stuff to move from one map to the other this will be a major pain, as you need to copy>open map>paste>close map for every single object you want to move...
good luck!
[if it's still not clear check out
this tutorial - that's where I learned this...]