I have noticed that recently my achievements tabs show the incorrect values in relation to how many achievements I have actually completed. Right now my 'Challenges' tab shows 0/36 when in fact 19 are complete. 'Bosses' indicates 76/84 when I have completed 80. The others appear okay and my total off 290/318 appears to be correct also so it's just a glitch with the tab headers.
Thanks for pointing out this bug SteveW. I am looking into this right now and will post a fix for it shortly. Cheers