edge loop mess

[alcachaz]

I am new to Maya and am trying hard to develop good habits from the get-go. Often times when it appears
I have solid, symmetrical quad geometry and I try to insert an edge loop, the edge loop continues around the
object, but sends off errant edges. In the attached image of the staircase, I simply want to insert a line dividing
the staircas in half vertically, but the resulting loop creates a pattern of diagonal lines. To create the staircase I:
-made a single step
-duplicated with transform 6 times
-combined the objects
-merged vertices
-attempted to insert edge loops
I assume this will be an easy fix for someone more experienced, but it is driving me crazy. Any help is greatly
appreciated. 

[joojaa]

Show the vertex mode.

[alcachaz]

Joojaa, thanks for the quick glance at my post. After hours of attempting to resolve this I got a hint from a side note in a 
tutorial I was watching. I believe the strange edges were being caused by shared faces. I was merging vertices without deleting
the faces they were sharing. Edge loops seem to be traveling the model cleanly now. In your experience, does this make
sense? Thanks.