Everytime I start 4coder the background is white. It takes about 5 sec. and it changes to normal. If I press something on startup it immediately changes to normal, too. Is this a common problem?

That is unusual. It sounds like it didn't paint the screen on startup, and so you see white. Then on the next event that causes repaint it actually shows up.

What OS are you running it on?

I use Windows 7 Professional N.

edit: I tried it on Windows 10 N and it's the same problem.