/testforblocks command doesn't work consistantly with stairs (possibly only corner stairs)

I was trying to compare two structures that used stairs and corner stairs, but no matter what I tried, I could not get the /testforblocks command to recognize that they were exactly the same structure. Then, I replaced the stairs with solid blocks and it worked fine. I then tried building an entirely different structure with stairs again but this time, the comparison only worked sporadically.

Basically, stairs don't work right with the /testforblocks command.