Stealth at end turn

When I end turn in games like ww2 and EU+, I can see other countries stealth until I press start turn? Is this a bug?

I think it is not bug.

No bug and only applies to stealth units involved in battles. More interesting to "see" these units are the lines indicating where they came from... possibly from a bigger stack.

I think you mean you can see stealths in turn 1 and in turn 2 they dissapear. i think that is for the 1st turn peace, when you press start turn 2 you automatically declare war, making stealths actually invisible

Peace with player does not allow to see his/her stealth units. Only in alliance you can see them.
If you see the stealth units of an opponent or player you are peace with, then it is because you are in view range.
When starting a new turn you can see he arrows of the units that are in battle with you; even the arrows of the stealth units.
If you have time, try to analyze them: from where do they come, what type of units, etc.