Actually, it does happen. And I assume that this is what the OP refers to. But it is not really a security check but more of an extra customs check (for drugs etc.). I got pretty angry about it the first time it happened (thinking I was mistakenly sent though the security check for connections).

To me this mostly happens when arriving from places like BKK or KUL (and strangely enough it happens less when flying SQ .) I have never seen this when arriving from Europe.