Conditional formatting rules split up when copying rows

e.g.
The sheet is occupied with data in A1:D10

There is a conditional format(CF) on B1:B10 to highlight duplicate values.

Now I insert row at 5:5 to make it A1:D11. Now the CF rule applies to B1:B11

Then I copy formatting of an existing row to the new row to copy the CF rule.

But now there are 3 CF rules: B1:B4, B5, B6:B11.

How can I add additional entries that share the existing rule(s) without splitting up the CF rules?