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when sent BTC
This is a confusing initial question. The other thought was the OP was waiting for BTC to be sent to him. Even if his Electrum has change address "clicked" another user can ALWAYS send BTC to the original address. That address never becomes invalid, its just that his instance of Electrum will never again use it while sending coins out in a normal use scenario on his end.
The "when sent" part of his quote makes me think he is waiting for coins sent to him. Do not fear if someone sends coins to your address repeatedly because you can still access them.
