Our JIRA instance had a lot of logged hours, before we started installation of Tempo timesheets, and as soon as the installation finished, tried to take a look at old reports using tempo reports, but was surprised to see no logged hours being shown.
Also, when looked at the issue detail view, the "Work log" tab showed no logged hours, however the "history" tab of the issue had a trace of old hours logged into it. Thinking the tempo wiped old time log out, we uninstalled Tempo, and the past logged hours immediately re-appeared.
Not sure if this is an issue with permissions I missed, or a default behaviour of Tempo. Please help!