Ah, search didn't work few days ago so I didn't bother to check.
If you capture enemy valor flag, your reinforcements get +30% boost as expected. But if your enemy captures valor flag back, your reinforcements lose about 60% of their health and probably damage as well(it's like you have lost both valor flags)."
Jesus Christ, February 22... That is 4 months since this bug has been spotted and reported in the appropriate forum.... and people bitch at me when I post that things don't get fixed as they should.