Selecting cells to verticaly merge is impossible with already merged cells in the column to the left

[bigsmoke]

Describe the bug
In the Avanced Table Block, selecing cells to verticaly merge is impossible with already merged cells in the column to the left

To Reproduce
Steps to reproduce the behavior:

1. Create an Advanced Table Block.
2. Vertically merge some cells in column x.
3. Try to select cells next to the merged cells in column x + 1 using Shift-click.

Expected behavior
Only cells from column x + 1 are selected.

Actual behavior
The previously merged cell in column x is also selected.

Workaround
This can be worked around by first merging the cells in column x + 1 and afterwards the cells in column x.