I have subfolders below my inbox. When turning on index synchronisation (what does that do anyway, keep a local index that is searchable?), it seems to list all email that I ever received in the inbox. The number next to the inbox folder is still correct, but inside there is suddenly lots of mail. (I purposefully only keep email in my inbox that I still need to act upon.) Turning index synchronisation off resolves the issue, but I guess all searches will be slower then.
Edit: I just did a search to test index sync and then deleted the query from the search field. I now cannot reproduce the issue anymore. Maybe it’s just a one-time bug after turning it on?
When you first start using Runbox 7 with a local index (which makes listing and searching messages instant), your browser will download the index from the server.
Depending on the size and activity of your account the index may not be entirely up to date, but this should correct itself after the next synchronization which should occur within 15 seconds (and indicated by a popup near the bottom of the screen).
We are in the process of adding more indexer servers to increase the index freshness, so this issue should decrease going forward.
In any event, the problem only occurs initially, as you have discovered.