[gizmo]

Yep in later versions it changed.
I use 3 column Light Lucid and I think most developers do to base there new designs as far as I know within 3 column light and lucid it has no altskin.css (As far as I am aware that's part reason why I base my footprint on the 3 column, less edits etc...and pure flexability with this design

What could of happened is for what ever reason you may have accidentally uploaded or altered something from admin area without realising it.

And I said to take a look..
Another option is to I suppose overwrite admin area, or reinstall saving your skin1, and uploading back up, there are so many options to correct this, and you need to decide... (What to do)..