When I change the speed of an edited sequence using Custom Speed, the clips all remains the same length, ruining the edit.

Hi. If I edit together a sequence and then decide I need to change the speed, if I select 2x Speed, for example, then the length of all the clips changes proportionately and the edit remains in tact. This used to be the case for Custom Speed too, but I must have accidentally changed a setting. Now, if I change a sequence to Custom Speed, each clip in the sequence changes speed, but remains the same length in time - ruining the edit. I then have to readjust every clip individually. It's driving me mad. Can anyone help please? Thanks.