Steps to reproduce:

1. Start In time-entries section, with a running time-entry. Then, edit it there and save it(this action will keep that time-entry as 'the active time-entry' in the context of the code)
2. Then, try to add a new time-entry, with a time posterior to that time-entry. You got the error.

This is caused because the initial active-entry gets cached, even though has been modified. A solution would be refresh the active-time-entry on edit.