I just noticed that when WinSCP (v3.8.1 Build 328) is run in second display and example some .php (or any textfile) file is opened to be edited in the internal text editor the window of internal text editor flips very strangely. It seems that window remembers correct height of last usage but width crops from last usage to maybe ~50-75 pixels. When WinSCP is moved to primary display and some text file is opened in internal editor the editor gets correct height and width values and the window is displayed as it should be displayed. And the interface style which is been used is Norton commander (in case you need this information).
Hopefully I descripted enought to get this bug fixed :)