@itsme 

I am using maple 18

For my case, both roman and Carl's suggestions solve the problem.

But anyway, thanks for the suggestion.

@Carl Love 

You are right Carl. I also think it is a bug.

And thanks for you suggestion. It also works perfectly.

@roman_pearce 

Many thanks roman. It worked perfectly. I also needed to use symbolic integration to keep evergything as exact as possible...and the good news is that what you suggested also works with symbolic integration

I was struggling with it for days. I really appreciate it :)