Same same, but different

Sometimes, through some twist of semantic fate, a word can acquire two senses with opposite meanings. Like 'sanction', which can mean to approve or condemn. Or 'fine', meaning merely acceptable or exceptionally good. There's a word for these. They're called contronyms, or alternately auto-antonyms.

A couple of weeks ago, there was a brief discussion on ThailandQA about the auto-antonymy of the Thai word รื้อ, which can mean either to tear down, as in รื้อตึก 'raze a building', or to bring up, as in รื้อเรื่องเก่า 'revive old matters'.

Another auto-antonym occurred to me recently: ป้องกัน. RID defines it thusly (my translation):

ป้องกัน ก. กั้นไว้เพื่อต้านทานหรือคุ้มครอง.
/pɔŋ kan/ v. to block, in order to oppose or protect.

So when you ป้องกัน something, you are either opposing it or protecting it. Quite different meanings. You can ป้องกันโรค 'protect against disease', or you can ป้องกันตัว 'protect yourself'. Here's a real life example of what can happen with careless translation of what I suspect was the word ป้องกัน in the source material. From a press release of the Public Relations Department:

Deputy Secretary-General of the Office of the Narcotics Control Board (ONCB) Pittaya Jinawat revealed points made in a tactical meeting with computer game related businesses focused on protecting and guarding against the pervasion of narcotics and also game addiction.

...

Game developers have affirmed that they are ready to produce more positive games that are age appropriate but also evoke family participation, which they believe will be the best way to safeguard deviant behavior. [Emphasis added]

I don't have the original Thai, so it's only a guess that the original word is ป้องกัน. But clearly they meant 'safeguard against deviant behavior'. What a difference a word makes.

Thinking more about it, there are other words that are sort of like auto-antonyms, but not exactly. For example, เหม็น. This word most commonly means 'to have an objectionable smell', as in ตัวคุณเหม็นบุหรี่ไปหมด 'you reek of cigarettes'; but it can also mean 'to find a smell objectionable', as in ขออนุญาตสูบบุหรี่ คุณเหม็นรึเปล่า 'Mind if I smoke? Does (the smell) bother you?'

It works similarly for หนัก, 'heavy/to find heavy': กล่องนี้หนักมาก 'this box is really heavy', vs. ยกไปเท่านี้ก่อน กลัวคุณจะหนัก 'that's enough to carry, I don't want it to be too heavy for you.'

There's something different going on with เหม็น and หนัก than with ป้องกัน, but I haven't thought of (or come across) a good way to classify it. Any ideas?