Attila Szűcs, one from hungarian LibreOffice developers (he's from NISZ team) made great improvements for work with merged cells.
I'll show you pair of images for illustrate it (left - 7.0, right - 7.1):
Select three cells, merge it (as shown on left image) and then try drag-fill columns down. A result was strange and very unexpected. Now in 7.1 it works as users wanted last 8 year, look at right image. It works for filling in to any direction!
If you want to have merged cells with some number sequences, then you got a result as on left image above (Merge A1 with A2 and A3 with A4, type 1 into first merged cells and 2 into second, select both and try fill cells down). But now in 7.1 all work as users could expect! Look at a right image above.