Why is typing a colon (:) in Xcode vim mode causing the Line Number pop-up to appear?

Title says it all. I type a colon when Xcode is set to Vim mode, and for some reason the line number pop-up comes up, as if I'd typed Command-L. Why is that? I feel like it didn't do this in the past; I could have sworn I used to be able to close editor tabs by typing :x. At any rate, this is incorrect behavior; jumping to line numbers in vim is done by just typing the number followed by a capital G. Is there any way to turn this off? I couldn't find anything in the shortcuts preferences.