I have received an Excel 2007 spreadsheet in which selected rows have been
hidden. When I try to unhide them using the normal methods, nothing happens.
The rows remain hidden. Also, I can hide additional rows in this spreadsheet,
and then cannot unhide them either. I can see that there are hidden rows,
because the row numbers (in the left-most column) are not contiguous. (This
effect is the same in the rows hidden as found, and in the rows I purposely
hid.)

There is something preventing the unhiding of rows in this spreadsheet.
Column hiding and unhiding, however, work normally. Any ideas how this
spreadsheet could have gotten into this state, and how I could force the
hidden rows to appear again?