SW 2015 SP 2.1 running on Windows 7

I have an extrude in a part that has the "from" property set to "sketch plane" I want to change this to an offset value, but the input box is greyed out. 

I tested to see if this happens consistently and it does not, if I delete the extrude feature (but not the sketch) and recreate the extrude with "from" set to "sketch plane" I am able to go back and change it to offset later.  Weird behavior, almost like the original feature was corrupted somehow.  I would normally be fine with a hack workaround like this but in this case it is breaking a bunch of child relations and causing me grief.  Would like to figure out how to fix the original extrude feature.  Anyone else seen this before?