Yes, I was thrown back when I found this 50 cents coin:

I thought it was just terribly beaten up but when I dropped it (oops), it just gives a wierd ring tone. I decided to confirm my suspicion and behold - weights more than 1 gram less than other coins that I have in my collection. Weighing at just 8.13g, I just find it odd. I guess back then, 50 cents was worth a lot more but you had dollar coins circulating.
Here's a genuine 50 cents in a mint set for comparison:

Singapore isn't too well known for counterfeited coins because of the strict laws but again, it just slips through. It doesn't hurt to be vigilant at all times even with common circulated coins.