Yellow Center Guides in Viewer: Flakey?

I've noticed that the center guides (the yellow lines that show up and allow you to snap your transform to center horizontal or vertical) don't always appear when you're using the transform tools in the viewer.

Does anyone know what the user has to do to get the snapping guides to appear/disappear?

It seems that if the guides show up, then <command> dragging your layer will turn off snapping.
I can't figure out how to turn it back on, though.

There appears to be no reference to this behavior in the documentation.

Cheers

They come and go, you're right. Bug.

Ahh.

I thought I was doing something wrong.

Thanks, Ben.

The guides work with positioning, and generally if you grab the image by the center point indicator the guides will appear.

Double Ahh.

Thank you, Tom.

I still haven't been able to find a reference to this functionality anywhere in the documentation.
It's a pretty cool feature- if you know about it.

Thank you.