I don't work for MS, but I can't believe anyone would make this a feature.

I'd guess it's a bug.

wal wrote:

Excel 2003

If I protect a worksheet and uncheck "Select locked cells" (i.e., so
the user cannot select such cells), this also prevents Ctrl-Page Up
and Ctrl-Page Dn from working to navigate from worksheet to
worksheet. Is this an intended consequence? (A bug?) There's no
reason to prevent users from navigating in this way.

--

Dave Peterson