I am unable to duplicate this issue.

For me, the beams are not broken when I copy a measure.

There must be something else going on.

Can you attach a picture of the measure?

Remember that you should always keep the bigger note value (e. g. a half note) in V1, and then launch V2 on the bigger note value, to enter the smaller note values (e. g. eighth notes) in V2.

Also, the V2 notes that are launched from a bigger note value in V1 (e. g. a half note), should not exceed the duration of the bigger V1 note value (e. g. only four V2 eighths on a V1 half).