Dialog and toolbox windows re-size themselves to full screen

I'm running a C# .Net program on a com开发者_如何学Cputer other than that I developed it on. It works fine, but when you open dialog or toolbox windows within it they always re-size themselves to full screen, which is really annoying as in the code I have set limits on the size and here they are being exceeded. This has never happened before on another PC. It also happens with some other programs, and even a pop-up dialog within Google Chrome.

I think this might be a registry setting but have no idea how to fix this. Has anyone else ever come across this?