I bought a 18 y/o Striker yesterday via Negotiations. He was 99%, and his Value was 15.3m. I didn't train him nor put him on the field, but later the same evening I started to train him SA and did a few sessions (he is 6/50 now). I remember him being 99% very well when I started to train SA because I specifically checked it.
But today, to my surprise, I found him being 100%! He costs more, as he should (15.7m) with this new quality. And, of course, now he gets a penalty to training pace due a new star. And no, I didn't put the training of SA on pause.
I wrote to support, but I guess they won't be able to help me.

Has anyone experienced the same bug?

This is him now:
Click image for larger version.  Name: Screenshot_20170215-115830.jpg  Views: 49  Size: 55.0 KB  ID: 77595