Connecting input and output GND of buck/boost -LED driver

Quick and easy: The datasheet of the Meanwell LBD buck/boost LED driver states "The output of LDB-L should not be connected to the input of th same unit or output from other sources." Any idea what could be the reason for that?

I am renewing a lighting installation of three LED group, each powered by one of those devices. I have a 5 wire cable going there. The original idea was to use 3 wires for + and one as a common GND wire, but the datasheet seems to forbid that. I could put the drivers at the end of the wire, but then they would be harder to reach in the ceiling, not neatly in the big junction box I prepared. Also, I would have to send the PWM control signal over 3 or 4 meters of wire ...

common grounds should be fine. The warning is to not connect the outputs in parallel.

No, that's misreading the datasheet which explicitly forbids connecting the -ve input to the -ve output,
ie this is not an isolated converter and does not have shared grounds. The circuit topology will be
optimized for cost, not your convenience. Also this is a constant current output so there has to be a shunt
resistor plus its associated voltage drop somewhere in there, bypassing that could prove disasterous.

MarkT, I am not sure who you are contradicting, Jiggy-Ninja (who says I can have a common -ve output net) or me (who understood I couldn't have it, be cause that might be connecting "the output of LDB-L [...] to the output from other sources").

I don't need to connect -ve input and output. I would like to have one common -ve input net for multiple drivers driving different groups of LEDs. But I guess you are right. +ve out could be regulated (i.e. not the same for different units), while the shunt could be between -ve input and output. In that case, I really couldn't have any common nets on the output side.
Guess the regulators do have to go into the ceiling.