In SE 14, go here:
Open the Tools|Options dialog.
Go to the "Languages\Application Languages\C/C++\Color Coding" node in the dialog.
Go to the "Comments" tab.
Select the entry for /*..*/ comments.
Check the "Nesting allowed" checkbox below there.
Repeat for other comment entries as desired.
Click OK.
Not sure why nesting is disabled by default, maybe some (presumably old) compilers still don't support nested comments.