Tax on unvested stock when leaving Singapore

[PNGMK]

I was wondering recently if the moving companies or the ports have some sort of notification system to tell the ICA and IRAS when people are leaving.
Two sets of families that I know, were stopped at the airport at Christmas and made to pay tax for the year (that was not due until April following year). Their EPs had not been cancelled and so IRAS should not have been notified, but both families had sent furniture/shipment to their own countries in the previous months. How would ICA have known?

Customs declaration with their FIN on it. I helped someone escape Singapore by shipping out their household AFTER they had left. (And yes, they did actually pay IRAS from offshore, they had other reasons to leave over night).

This is a bit disconcerting.

Educated guess only.

[zzm9980]

I just called IRAS and asked them about tax clearances, outstanding sums owed, and leaving Singapore.

From the horse's mouth:

When the company files an IR-21, IRAS will notify the company how much is owed. If the amount being withheld by the company is not sufficient to cover that amount, a notice of payment will be sent to the individual. There is a payment due date of 10 days in the future on that voucher. If you do not pay by the due date, then IRAS will file with ICA to prevent you from leaving Singapore. You are allowed to come and go from Singapore anytime after the IR-21 is filed, and if you owe money during the 10 days between notification and the payment due date.

[PNGMK]

I some money when the group I work for was bought by another group (NYSE listed public company taken over by another NYSE).

The transaction was "cashless option vesting". In other words I had options that vested due to the sale - the company arranged for this to be a cashless transaction for me - in other words I received the difference between the share price before the sale day and after the purchase. However in legal terms I paid for the shares and then they were sold by me to the new owners at a much higher price and I received obviously the difference.

Is this capital gain in Singapore? It would be in Australia and would be treated differently tax wise. What is the tax rate applicable? Any guesses?