What caused my brick column to crack

I need help determining what went wrong. I just built my fence at each end I made a brick column. The first one I completed suddenly developed a crack down the side of it. I am not a mason, but I took my time and did a nice job. After a few days I noticed this crack that has grown to be 1/16" or slightly larger. How I built the column was by using a pressure treated 4x4 and simply wrapped it with brick. I did pack between the brick and the post with mortor. (I assume that is the problem). I had built a second within 2 days or so of the first and it has not cracked and still looks great.
The problem is that I have 2 more to build and need to know what caused the cracking so I don't duplicate my errors on the next column. Please give me some advise.
Thanks
Tex:NO NO NO:

 

The moisture in the mortar caused the 4x4 to swell and crack the column.

 

My first guess is that the PT started to twist as it dried out in the heat and pulled your brick work as you said it was basically connected. Normally what I have seen is that the PT is simply wrapped in poly, with no mortar against it. You also did not mention what base you sat the bricks on. Is it all just sitting on a shallow pad, or is there more substantial footings involved?

 

However, my PT has been drying all summer and has been standing for a month and a half so it should have been dry. The interesting thing is that one post did it and the other did not. There is one difference. The 2nd column I did in 2 settings. The first column I did in multiple settings as I would do a few rows as time would allow. The significance of that is I would wet the old brick when I started so that it did not absorb all the moisture from my mortar. I probably got the first post much wetter as a result than I did the 2nd post.
I poured a concrete footing when I set the post originally. The footing still looks great.
I soak my bricks in a bucket of water before setting them. Is that a bad idea? The next post I am using will be galvanized metal from an old chain link fence. These support a large gate. I intend to fill between the post and the brick with concrete/ mortar mix. Can anyone see why that would be a bad idea?
Thanks for the help gents.
Tex