Merge cells bug?

Dear author,

I just want to thank you for this great plugin. I have just installed and started using it, and I found something which I don’t know if it is a bug or not. It is the merge cells feature in the advance table block.
When I merge the second column’s fields using SHIFT (see image), I cannot merge both fields of the third column. I tried SHIFT or CTRL and none of them worked. This is what it shows when I select both fields from the third column. It selects everything from the second column, third column and part of the fourth column. Why is this happening?
I thank you if you could help me.

Chen