drop a segment erase data?

I restored a user db on ase 12.5 and then check the segment information for this db, looks like the device list for this segment totally messed up.

For example, on live, segment myseg has 2 devices(by extend), but on restored db, this segment now has 3 devices in the list.

I try to extend/drop device from the list so that it is same as live, but it only allow me to drop:

sp_dropsegment 'myseg', 'mydb','dev1'

not allow me extend segment by:

sp_extendsegment 'logsegment','mydb','logdev'

so want to know if sp_dropsegment will erase data? and this is because of I did not restore master before restore mydb? actually, there is no change about the segment.