Here is an example of this problem showing itself.

I have the object shown below (not a real object, just a manifestation of the issue I'm having on more complex shapes) :

I wish to add radii of 10mm to the two lines shown below :

Now, when I go to do this, regardless of whether I add the radii in the sketch or as a feature, they will, while I add the feature, show themselves as curves. This is fine, and as I want it to be.

However, when I finalise the feature and look at the part, this is what I see :

If I highlight the feature I will even get shown the curve again, but I cannot get the part to permanently adhere to it :

If this were only an issue of visualisation I wouldn't have a problem, however when I then save the part as a .igs or .step, those files will show these straight lines rather than actual radii!

I'm hoping there's a simple fix to this. Can anyone help me?