Form Size problem

Question

I'm making some application, and i work od that project on two computers paralel.. at the first i have Microsoft Visual Studio 2008, and on the other I have Vis. Studio Expres edition 2008.
I don't know if that is the reason.. but every time i click Start Without debuging, or start debug,  the size of the main form change (it just change just like that, it get smaller) for example it i set it to 800x600 at the property grid, when i start the application it become let say 800 x 580 or something...
application has more forms, but that is happening only with main form..
i can solve this on form load.. but i want to know what is the reason for hapening that..
is that some bug or what?? does someone ever had same problem? please, every opinion is wellcome..