I noticed too, on a fresh install the red marker line (Ctrl + L) appears in the status window when you first connect.

That's not a bug. Some of the default options have been changed in this version, this is obviously one of them.

I couldn't find it in the 'whats new'
just seems strange to have that enabled imo

It doesn't seem to be mentioned, but I noticed that the treebar is enabled by default in this version and so is logging. It seems like many of the settings have been changed so that some of the lesser known features are available straight away.

So now it's like what Microsoft does with all of their products, have every option enabled by default so as to make sure the user knows it's there?

This is the most annoying default feature

Khaled -- Please shut it off.

You want Khaled to come to your house and adjust a setting on your computer for you?

These new features are only enabled by default once. Next time you upgrade (and keep the same mirc.ini), they should not become active again. This is done so that you can see that a new feature exists, and then choose to keep using it or disable it.

-genius_at_work

While I agree this is not a bug I personally don't see the need to enable this feature by default, specifically because it's not very helpful to most people, and can be annoying for many. Also, this is *not* a "new feature", so giving it exposure doesn't sound like a great reason to default it.

Also when I turned it off, the marker turned off only on the channel a had active, other channels on other networks still had the marker until I restarted the program.
I've also had no luck turning it back on without a restart of mirc.