OK, in the meanwhile I tried a different approach, as I am afraid, that this might be a bug and I can't wait for that.
The issue is, that certain members in a pool need to get a Cookie with a longer expiry-date (I know, from the above, it seems to have nothing to do with this), so I tried the following iRule:
when HTTP_RESPONSE {
if { [HTTP::cookie exists "Cookie_Test"] and [HTTP::cookie value "1718485258.20480.0000"] } {
HTTP::cookie expires Cookie_Test 18144000
}
But this doesn't work. There's some logical error in it.
On the other hand I am afraid, that with this iRule I just will have the same problem, that the cookie doesn't get updated.
What I really would like, is a way to just assign a modified cookie when a specific member gets used, but I am afraid, that this is not possible.