I've just noticed that I can't seem to activate Oldstyle numbers in some fonts like Arno Pro when using Illustrator CS5. For the longest time I hadn't realised that Arno Pro even had Oldstyle numbers for this reason, but after using it in Indesign I've realsied it does.
I can open up my glyphs palette and individually insert Oldstyle numbers into text but this is obviously pretty tedious and likely to cause mistakes and not the way the typeface is intended to work.
I've tried other typefaces such as Archer and I can still activate Oldstyle numbers from the Open Type pallette.
I'm stumped as to why this doesn't work and I can't seem to find any other info on.