It's random, that's why. If you got 1 message for devfee, then it works.
As I said in my last post, in 5 hours I had 9 DevFee shares out of 342 total shares, that's 2,63% fee of my shares.
In your screenshot you had 1 DevFee out of 50 shares, which is exactly 2%. I imagine you only run the miner for an hour or so though? That's a pretty small sample to draw any conclusions.