Talk:Quests/@comment-11970459-20140607160156/@comment-24980562-20140607162443

Nah, that's normal.

Technically speaking quest D7 潜水艦派遣作戦による技術入手の継続！ requires you to do expedition #30 four times, but already counts the previous two times you did #30, so when you get the quests you're already at 2/4 a.k.a. 50%. When you finish it a third time you've done 3/4 of the quest, and since 75% is obviously lower than 80%...

tl;dr

Do #30 one more time and you're done.