When greater than 10% of your flags handled in the last 7 days have been declined you'll get a notice in your flag dialog indicating that some of your recent flags have been declined:
Attention: some of your recent flags have been declined - please review them before flagging this post!
This would suggest that your recent flags are where the problem is, however by clicking through the link to review your recent flags the heading makes it clear that it's your recently declined flags that matter (as in, the date the flag was declined is important, the date the flag was raised is not):
Flags raised by Nick which were declined in the past 7 days
For example, I have raised 6 flags in the last 7 days (or 8 depending on where you start counting), all marked helpful, however yesterday a flag I raised on July 10th (18 days ago) was declined, which has resulted in the warning being shown.
Can the text in the notice be updated to correctly indicate what has caused it to be shown (note that "recent" has been moved to affect the action of being "declined" rather than the "flags"):
Attention: some of your flags have been declined recently - please review them before flagging this post!