Kesa also asked the same question. To me, there is no break in service when one is on no pay leave. He should be entitled to 18 days for every 12 month service. Consult the Labour Department for an official answer.
KL Siew has put up a sister site by the name of mylabourlaw.net, which is in effect a more user-friendly version of the present popular pesaraonline.net. The site is in the process of being fine-tuned but it is fully functional. You are invited to visit the website at http://www.mylabourlaw.net and give your views or suggestions. Queries can be posted and be responded from there as usual.