SA tax law is residency based. Hence "resident for taxation purposes" is as defined by your days in the country, as stated above. (Note: not where you sleep, where your house is etc etc)
If you are non resident for taxation purposes, you do not pay SA tax on your foreign income. In my case, I still had to pay tax on SA rental income, though I am non-resident for tax purposes.
It does not matter what the earnings are (on duty/off duty/allowance etc etc) or where they are paid - they are all seen as income
If you find yourself paying double tax as a result of this, you can get a tax credit offset if the country you are in has a double taxation agreement with SA. Australia has, for example
(Sorry, this effort is double posted - finger trouble -pesky "control" key)