There was a bug in 7.0 that caused this in duplicated timelines – it was solved in 7.0.1 as far as I know, so ensure you have the latest version via software update.
Otherwise, if it happens a lot you have a bad install, or your FCP preferences are corrupted, or both. Use FCP rescue or FCP maintenance pack, and reinstall the whole suite from scratch if possible – this is one reason why an edit system should not have a lot of other software on it.
I can assure you this is NOT typical behavior for FCP suites.
Edit Out Ltd
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FCP Editor/Trainer/System Consultant
EVS/VT Supervisor for live broadcast
RED camera transfer/post
Independent Director/Producer
https://www.blackmagic-design.com/casestudies/detail.asp?case=therydercup