Before all 6 patterns were done I was occasionally getting triple perks in both columns. However, after getting all 6 patterns I noticed that I always get 3 perks in 1st column and 2 perks in 2nd column. For example, this week I did all master challenges once, then bought 12 weapons, 17 in total. All of them had 3 perks in 1st column and 2 perks in 2nd column. There is also [url=https://www.reddit.com/r/DestinyTheGame/comments/1eavyoa/do_not_rush_to_complete_patterns_for_salvations/]a reddit post[/url] about this issue confirming that it is not an unluck, but a consisting behaviour.