Did my NOID get sunburned?

[Acharn]

I bought this monopodial with two others about four or five months ago. I don't know why I didn't take pictures of it when it was in bloom -- I usually do. Anyway, I've been trying to give my monopodials more sunlight, and they seem to like it, but none have developed flower spikes yet. I suspect they're spending so much enerby growing new roots they don't have any left over for flowers. I live in Thailand, and the sun is very strong around noon. During the rainy season (May thru October) there's usually a high haze that modulates the sunshine. A couple of others seem to be doing well, but I noticed this discoloration. I've moved the plant to a shadier location, but can't be sure this is actually sunburn. I don't have enough experience with vandaceous types yet.