Repetition include_end_by extend one day on edit

Hi, I 'm having a problem with include_end_by.
Suppose I create an repeat event with end by on day 25 (with include_end_by on true)
Then, if I edit the event in the lightbox the “end by” textbox is 26.
So if I save again, the repeat event has been extended one day…is this a bug or i’m doing something wrong?

Thanks for the help!
(And sorry for my bad english haha)

make sure you use the latest version of dhtmlxScheduler. I couldn’t reproduce the problem with the package downloaded from site