I don't know if this has already been noticed or not but there appears to be a bug or an issue with the multi-add function in groups, whereby using shift to select Dragons after using the 'Filter Dragons' box will add multiple unwanted Dragons. I also wasn't sure where to post this so hopefully this is the right section.
I created a new group and selected the top three Dragons using Shift or Ctrl and added them to a group. As you can see they are the only Dragons in the group.
Then I went to 'Add Dragons' and used the filter to limit the Dragons showing up, after which I selected the top three again. If I used Ctrl then only the top three would be added. If I used Shift then it would add a load of extra Dragons alongside them, 131 in this example.
I'm not certain but I would guess that the filter is only limiting which Dragons can be seen, not actually removing them from the list. Since using shift selects all of the Dragons between the two points selected you can select Dragons that you have filtered out of a search via the shift key, as the dragons are only invisible and not completely removed.