Ok, let's set a few things straight.
.....apparently this is a result of ATC requesting it.
No, ATCs didn't request it. Not operational controllers at least.
This was something inserted in the FMS coding by the PANS-OPS procedure designer to (supposedly) mitigate the risk of conflict with Macau departures over the top of CLK (which enter HK airspace not below 6,000 ft) in the event of you having a radio failure after becoming airborne and climbing in accordance with the procedures in the AIP (ie after the next waypoint unless there is a restriction).
The reality is most Macau departures are well above 6,000ft and up up and away before any HK departure could hope to get near them.
Now, I agree that there is some degree of ambiguity (for the controllers as well) in that the coding and the text description on the SID plates does not line up. There is no mention on altitude restrictions at waypoints other than the "climb initially to 5,000 ft".
Despite considerable discussion both internally and with the major carriers, the decision has been made, rightly or wrongly, to keep the coding as is.
Personally I think it needs tidying up.
On the subject of "maintain .....", the practice is what is taught and expected of operational controllers in ensuring separation is maintained when there is the likelihood of a breakdown occurring
if the aircraft were to continue on their current trajectory. It is referred to as Separation Assurance.
Just as you receive TCAS TA/RAs, our controllers receive Predicted Conflict Alerts (PCAs) and Conflict Alerts (CAs) from the radar system, if a potential or actual conflict is detected based on the current trajectory. This causes the aircraft labels to turn red on the radar screen and highlight the level at which a breakdown will occur.
Just as you have procedures/call outs when you get a TA/RA, our controllers are taught to follow standard practice and reiterate the assigned level as a risk mitigation measure. It is also a double check for the controller that they have not inadvertently assigned a wrong level which has gone unnoticed.
Given the amount of crossing traffic within the FIR (we have a total of about 1,700 flights per day now) it is inevitable you will receive these calls several times on the way to the FIR boundary from different controllers.
One would hope you appreciate it's done for a reason, not shear bloodymindedness or controller ammusement.