Hi Jacky,
Thanks for using Syncfusion products.
I am afraid that I am not able to reproduce the issue you have mentioned here. I have used the same code snippet to set the font size that you had mentioned in your post. I am getting the font size only in 8 point, in the output html code.
Please refer the Screen shot from the below link, which illustrates this:
http://www.syncfusion.com/support/user/uploads/font_ca4b0b71.pngPlease have a look at the above, and if still the issue exist, could you please send us a sample to reproduce the issue? so that we could sort out the cause of the issue very soon, and provide you a better solution.
Regards,
Raji