[Beta patch issue]
After EVERY battle (without exceptions) guest player disconnect from campaing right after he saw victory screen.
If he connect to host right after that - victory screen appears again (against unknown enemy) and u get experience. If he do that again - victory screen appears again. Using that method players can develop, for example, last level and access to battleships right after first battle in campaing.
If battle happen during enemy turn and after battle - enemy do some movement - after guest player connect enemy do their movement again.... and again... and again. Looks like every time when guest player connect - processing new enemy turn started (but number of turn displayed in UI not change)