This is not a bug, but by design and the feature-request to change it got declined long ago Don't display pending edit counter if you've exhausted your suggested edit votes (the situation slightly changed and there is another request Don't display suggested edit counter if you've exhausted your suggested edit votes but I think the main reasoning there still applies).
The theoretical point to note is that it is intended not as a notification but as an information. That counter is not a call to take immediate action, but it merely informs you that it might make sense to visit the review-queue. I know that for suggested edits it might not really much feel like this in practice, but 10k+ users get the (cached and approximate) count of all review tasks there, to them on this site there is basically always some number there.
The practical point to note is that it would be difficult to change this, or maybe difficult is not the right word, but rather it would be expensive performance-wise to determine the number on a per-user basis rather then to show one number to all concerned. Note that if you suggest edits yourself you will also increase the counter while you cannot possibly review them.
To sum this up: Treat the counter as information not as notification, and ignore it when it is not relevant to you at this point in time, for example as you know you are out of reviews.