open and euid security flaw in 5.0-Current?

[Killing]

On a FreeBSD 5.0 the behaviour of screen when connecting to other
users sessions have changed. Previously:
1. login as userA start a screen as userA and disconnect
2. login as root su - userA "screen -r"
3. result failure as userA cant access the ttyX with such a message
Current:
1. login as userA start a screen as userA and disconnect
2. login as root su - userA "screen -r"
3. result failure as userA cant access the ttyX but no message

After looking around in screen's code I found that after doing a
seteuid( userA ) an open on root's terminal is still succeseding.

Surely this is a problem as when running euid userA there should
be no access to ruid's files?

    Steve / K