Deleting selected table cells corrupts table

Summary of The Bug

Confluence 4.0 editor in Firefox shows a bug where on table editing where it deletes whole cells instead of just emptying them.

How to Reproduce

1. Create a 4x3 table
2. Enter some text in the cells
3. Highlight the content of three cells on one row
4. Delete
5. The highlighted cells are deleted instead of just their contents

Refer to this video for the detail