Confused item counter for inbox

After putting items into the inbox using a script the item was not incremented. When removing those items the counter is decremented, resulting in a negative value.

Is there any means to fix the counter?
And: what can I do to avoid this issue?

Thanks for any feedback!

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The item counter was reset after cleaning the waste basket. That’s fine, but I don’t understand yet why it stumbled.

I also have a negative number in my global inbox. However, I suspect mine may have something to do with the use of Dropbox.

Please advise.