It is not possible to merge 2 filters when they are not in the same selection.
If you select 2 filters that are in different places in the list and not
adjacent it will simply copy the first one twice into the merge dialog.

Created an attachment (id=7938) [details]
2.7.1 prerelease 1

Apparently there was something wrong with the function "getSelectedFilterAt".
This might also affect other functions that work with multiple selections (such
as sort by alphabet)

This version fixes the problem.

Tested and seems to work. Successfully merged 2 filters that were not next to
each other.