[Gambas-user] How to set a slider value?

[Aleksandrs Livshics]

Dear Gambas users,
I am new to Gambas and my question may be silly,
however I cannot find how to set a slider value in the 
code. (Not the initial value, this is easy)
I want to specify some event (like double click on a slider)
to force it to jump to a predefined position/value.

If I write Dbl_click() method and use something like 
My_slider.value = The_value
in it, then slider on screen does not move from where
I have set it previously with a mouse. More precisely, 
It jumps to a position which corresponds to The_value
and back to where it was before!
Any ideas would be helpful.