HiDPI (High Dots Per Inch) displays are screens with a high resolution in a relatively small format. They are mostly found in high-end laptops and monitors.
This is a Microsoft Windows issue -- actually, a driver issue -- and not related to forex:
FSB-Pro is developed using Microsoft's Visual Studio development environment. When a Windows application runs it makes calls into .NET Framework which, in turn, call into the Windows OS which, in turn, calls into driver code. There are software drivers for every device attached to a machine -- including exotic display adapters. The primary purpose of an OS is to hide nitty-gritty details of the hardware and relieve the developer from having to worry about these details. Furthermore, there are zillions of different types of hardware and most hardware manufacturers consider their designs to be proprietary. It is impossible for developers to have to deal with the myriad of hardware configurations out there (however, it wasn't so long ago we did have to). The modern solution is "software drivers" -- these are usually developed by hardware manufacturers and distributed freely. When you install Windows it already includes thousands of software drivers for common devices from major manufacturers. However, for new hardware or hardware from less well-known manufacturers, it is left to the user to manually install the needed (or latest version) software driver.
If the hardware doesn't work properly -- especially a device as common as a printer, or display, or speaker, or network adapter, etc -- it's usually a software driver issue and something an application developer has no control over. The fact that a "compatibility mode" improves the situation is another clue it is a driver issue. FSP-Pro knows nothing about "compatibility modes" -- it's the same FSB-Pro code running in both situations. So -- if compatibility mode makes a difference then that means the behavior is affected by the Windows OS (and the drivers it relies upon).