This problem has brought my research in ancestry to a a complete stop. It is maddening. Aren't there other people other than we few with this problem? I can't believe this is a user issue, as ancestry always wants to suggest (ie "just clean your history file").
I tried entering a large family of 10 people in a pre-1880 censu by hand. It was extremely cumbersome. Even with copy and pasting the Residence Fact for the census, you still have to enter a name fact and birth date by hand for each person in the census from the one that you originally searched for. It is almost as bad as the old days when I had to actually go to a library and get census info from micro-film machines - but not quite.
This effects more than not being able to post other family members into one's file. One also can't "drill down" into later children's families as adults by using the "suggested links" in the right panel - because the merge box is locked. Also, one can't jump from 1850 to 1860 to 1870 to 1880 census because, if 1850 is your first census, the merge box stays locked on the 1850 census. You have to backtrack to the "all results" page and then refind the next census where the family might be. Frustrating to the max.
This cropped up a couple of weeks ago just for a day or two. Then appeared ok. Then started again yesterday.