I'm on SW2011 SP5.0 and I have no problems adding +.015 after the diameter dimension. It will still add it to the existing value.
I see what you mean. I am running SW 2012 SP1. When I try to use a math function on the Counter-sink diameter, for instance .385+.005 for the counter-sink diamter, it does not evaluate when you hit enter or click in another field. Upon hitting the confirm button (the green checkmark), the value is updated.
I think there was a time, maybe prior to SW 2011, when it would evaluate from within the Hole Wizard PropertyManager. Strange...
What Operating System are you using? I am using Windows XP with SP3. I've been getting the feeling that even though SW says they support XP, they are much more focused on ensuring that SW works for Windows 7.
I am using 2011 sp4 in vista 64 bit.
We are not on maintainance so I cannot write this up as an enhancement request or a bug.
I don't plan to upgrade to 2012 for a few months yet.