I'm working on tailoring on my toon which has 100/25/100 (str/dex/int). Strength and Int are both pointing up, Dex is pointing down. I just gained in tailoring, but lost a point of Dex so now I'm 100/24/100.
Im guessing you got a stat gain in str or int from tailoring. You can still get "gains" as 100, you just dont get an increase, you still get the decrease in what ever stat is pointed down. Same thing happens when you have 100dex/100str both pointed down and are at 700 total skills with every skill pointed up. If you spam a backpack and phantom gain snooping for dex gains with your INT pointed down youll randomly lose INT.