I have not seen sunburn on a VFT. Maybe it is because I grow most of them indoors or with tons on shading in the Texas Sun.

The thing that concerns me is the temperature of the soil. You really do not want the soil temp to get over 90 degrees. If that happens you take a chance on damaging the roots.

That might be the effects of what you are calling 'sunburn'

I would not recommend putting these plants out in the sun without some shading.

Indoors is one thing, but outside is something else.

The black spots and stunted growth to me says root damage and not sunburn.

The effect of root damage can take a week or longer to show.

FYI:

The soil temp will be different from the air around it. If you have it in water, or a slightly bigger pot ( 4 inches ) this will help to curve it some.

Though I would not recommend repotting in the growing season, I would wait until the winter or next spring.

Or, just as good, give it some shade [img]http://www.**********.com/iBhtml/non-cgi/emoticons/smile.gif[/img]