This used to work in 2.6:
(this strange code is the effective result of running squeeze on a null piddle)
It now returns an error:
slice: slice starts out of bounds in pos 0 (start is 0; source dim 0 runs 0--1)
According to the slice docs,
"", ":", or "X" -- keep The empty string, ":", or "X" cause the entire corresponding dimension to be kept unchanged.
So I think the new behavior is a bug. Certainly the old behavior was very useful.
I'm afraid my PP is a bit rusty today, else I'd suggest a fix. My apologies.