Hit another old bug (oh I love when the game wants to remind me of all the old annoyances), again I still run the frogbuild so it goes in here (and I DO hope Frog is actually reading this
).
Was designing a juggernaut, finished Designing my juggernaut and after that I tried to design a juggernaut using a different weapon (so I could have a little bit of everything available to me).
Thing is, with the new juggernaut I was locked down with 2 traits I could not remove!

I then tried to exit the design screen, exit city screen and clicked on my unit, and then reentered the design screen and the bug persisted! I didn't try to end turn as that was not the point...
I hate it when I am locked out of options like this... as you can imagine 
grabbed the debug too, incase its important - https://www.dropbox.com/s/trtib8j60mc6yg6/debug%20%2815%29.err
PS. don't mind the picture's name I "forgot" to rename it when I opened my image in my screenshot folder to paste the screenshot
(I don't use the screenshots FE dumb to somewhere, and frankly wish I could turn that off, I go in manually and paste it in an image file... old habit
)
Edit: Happened again after I restarted the game, am trying to design a few different juggernaut designs for the AI so they aren't all using the same weapon and same traits... Grr 
Sincerely
~ Kongdej