twincast doesn't function well ... i think

How does it function Twincast .?????
If i play after have played another spell(when it's still in the stack) twincast tell me to copy the last spell but when they realize ... the copy does nothing ???
Am i wrong in playing it that way or it is the program???
If i play after have played another spell(when it's still in the stack) twincast tell me to copy the last spell but when they realize ... the copy does nothing ???
Am i wrong in playing it that way or it is the program???