Not quite correct.

I used to have the same problem. Couldn't figure when or why it happens and still don't. I do notice that it will happen everytime I upgraded the firmware. Firstly to 4.3 and then to 4.3.1, 4.3.2 and 4.3.3.

What worked for me may not work for you. The problem for me was that I keep the mobile data switched off (I prefer to use wifi). So whenever the usage = standby time happens what I will do is switch on mobile data. I will leave it on for a few minutes and then switch it off. The standby time will now continue ticking but the usage time stops. Works everytime so far.

My theory is that something seem to be running in the background trying to send/receive data using the mobile network. Since I have it on off, it cannot do that and will go into a continuous loop which shows up as usage time even though the phone is in standby. By switching on the mobile data, the problem code will be able to complete its data send/receive and shut down. So no more unintended usage.

I'm using an iphone 4 by the way.

There are various solutions suggested. Some work for others and some don't. No one knows why because everyone's phone is different. There is a list of suggested solutions here: https://discussions.apple.com/thread/277731...rt=589&tstart=0. Quote from that:

0. Run the battery all the way down until the phone shuts off, then charge with the wall charger for 4 hours to recalibrate the battery gauge.

1. Reset Network settings and reboot (Hold HOME and SLEEP until you see an Apple logo, ignoring "slide to power off").

2. Reset All Settings and reboot.

3. if you have any push accounts open Settings/Mail,Contacts,Calendar, tap on the account name and turn the 3 switches off. Back out of Settings. Open Mail, then Contacts, then Calendar to clear pending operations. Reboot. Then go back into settings and turn the switches back on. This clears stale connections to the Exchange server that consume data and power but do not pass information.

3a. If the problem still exists actually delete the Exchange account, reboot, and add it back.

4. Turn off Notifications and reboot. If this fixes it find the app that is sending data when it shouldn't. It will be an app that updates on its own, such as Facebook and other social networking apps, news apps, etc.

5. Kill all programs in the Recently Used ribbon. A long shot, but sometimes it helps.

6. Disable Game Center and Ping in Settings/Restrictions. These can use data and reduce battery life. If you actually use them after disabling them reboot, then enable them again. It may be a stale connection problem like Mail.

7. Disable Find my iPhone. Same as above. Likewise for App Store and iTunes store. Also a long shot, but some people have reported success.

8. If you've gotten this far go to Settings/Reset and Erase all content and settings, then Restore as a new phone without reloading your backup. Do not install any apps or set up email accounts. Test for a day. If this does NOT fix it contact Apple for a replacement phone.

9. If it DOES fix it try reloading your backup. If this breaks it redo the restore and do not reload the backup.