TH1F::Add with integral option

Dear experts,

I was playing around with the TH1::Add function and
found something strange that I cannot figure out.

I define a standard gaussian TF1 and add it to a TH1F
with and w/o the integral option.

The TH1F with the integral option is asymetric and the bin contents are ~2.2 times
bigger than expected (and hence the integral is also too big).

I have attached a simple macro to make clear what I have done.
Whats wrong?

TH1F_Add.C (554 Bytes)