Why activity bars are splitted after schedule

Hi, every body.

I'm encountering the follow problem:

after schedule the activities bars are splitted / divided.

I've used :

- Physycal % of calculation (insert the % value)

- I've used the  setting an expexted date and not 

- not any resouces are loaded

- all links are FS =0

- there are not constrain

i20_split_a.jpg

Pleas, somene can tell me why this happen,

thanks

Pierfrancesco