Thanks for letting us know. It is never a good idea to have tho copies of Electrum wallet installed on the same computer since they share data files.
This Electron Cash forked wallet apparently goes even further.
Yes, the approach with moving your BTC elsewhere first before opening wallet for BCH is the most prudent.
Two reasons:
- to assure that both bitcoin varieties have their own addresses and data files
- to use different seeds for the wallets