External applications opening Safari links in new window rather than new tab

I've noticed that when an application, such as iChat or Twitter for Mac, sends a link to Safari it opens in a new window rather than a new tab. I can manually force it to open in a new tab by holding down cmd, but I'd like this to happen automatically. I don't recall links opening in new windows in Snow Leopard.

To be clear, I'm not talking about opening links within Safari itself, I've set these to open in new tabs already. I'm talking about external applications sending links to Safari.

In Safari > Preferences > Tabs, there's a preference for setting when pages should open in windows or tabs.

Look here:

1. Open Safari > Preferences and select Tabs along the top
2. Under the option for "Open pages in tabs instead of windows:" select "Always" from the drop-down.

This will force every application to open links in tabs.

So this is strange - I just got this to work.

In the above window I set "Open pages in tabs instead of windows: Always" and then I unchecked the option for command-click opens a link in a new tab. After doing that - links from external apps opened as a tab in the same window.