zonoma, you have to look at it from the flight crew's view too, if they are on a heading how do they know when they will get "own navigation"?
They cannot second-guess whether it will be to the original point where a restriction was expected or to somewhere beyond.
If that happens before the original restriction point but they are sent to the next elsewhere, that is a new clearance so cancels any expectation of "level abeam" unless the ATCO reissues that requirement.
As I have just finished my 30+ years in NATS, I leave the job rather dismayed at the almost complete disconnect these days between ATCOs and pilots, to my mind it would be a great idea for NATS to use 2 of the "additional attendance" days to send people on compulsory familiarisation flights.