Redirect Helper

$1 works, but $2 doesn't?

Hello from Hamburg, Germany!

I want to inject a sub-parameter into an URL via REGEX. It seems to me that $1 works, but $2 does not.

Rule condition ist defined as:
If request URL REGEX https://securepubads.g.doubleclick.net/gampad/ads(.*)cust_params=(.*) Redirect to https://securepubads.g.doubleclick.net/gampad/ads$1cust_params=demo%3Duap%26$2

Tooltip says: "$ digits ($1 to $9) can be used to insert the corresponding capture groups"

This should insert 'demo%3Duap%26' at the beginning of the value of key 'cust_params'.
Therefore i expect URL
https://securepubads.g.doubleclick.net/gampad/ads?one=a&two=b&cust_params=subone%3Dc%26subtwo%3Dd%2Ce&three=f&four=g
with $1 = ?one=a&two=b&
and $2 = subone%3Dc%26subtwo%3Dd%2Ce&three=f&four=g
to be redirected to URL
https://securepubads.g.doubleclick.net/gampad/ads?one=a&two=b&cust_params=demo%3Duap%26subone%3Dc%26subtwo%3Dd%2Ce&three=f&four=g

However, the resulting URL is
https://securepubads.g.doubleclick.net/gampad/ads?one=a&two=b&cust_params=demo%3Duap%26$2

Is this a bug in the software or an error in the way I try to use it?

mvhJJ