Javascript regex is not accurate, sometime is true, sometime is false

Question

I have a regex:

a=/((09|03|07|08|05)+([0-9]{8})\b)/g

And a string here:

b="0977466666"

Then when I try to use a.test(b), sometime it is true and sometime it is false and I do not know why but if I omit g flag, it is always true.