svn blames Bo for removing the feature in rev 15990:
Me again? I won't touch anything in the core ever again! :-) Rev 15990 is to fix bug 686, i.e., remove empty cell from within. We have discussed this patch many times and there was no consensus about the intended behavior of backspace. The described behavior was intentional and was considered appropriate by some. (BTW, if you have an empty numerator, backspace will simply go left, not touching \frac.) Bernhard, could you give an example why this change of behavior is inconvenient to you? Cheers, Bo