broken page when adding row in dynamic table

The two tables are dynamic. Add/Delete Row can work. They are both located at the end of a page. I've arranged them in flowed subforms:

All subforms in the picture are flowed, Direction: Western Text.

Problem:

When I add row in section 1, section 2 will go to next page like this (the grey bar means page break):

When I add row in section 2, it breaks like this:

I'm expecting two sections to flow together, that's why I wrap them into the subform "Section_1to2". But it still doesn't help.

How can I update the structure of the two sections? Put them into one table, and use script to display/hide the table border to create a false image of two tables? This idea scares me at the thought already.