Operating system: mac osx 10.14.4
Graphics card:NVIDIA GeForce GT 650M 512 M
Broken: 2.81 alpha 3d8f1586973b nightly build 2019-08-21 and official
Short description of error
possibly related to t68647. "objects selected using box select cannot be moved to collection if there is no active object"
the rest of this will be very similar to that issue (now resolved for that specific case).
If you have a number of objects and select one then delete it there is no longer an active object or previously active object.
If you then use any of the selection tools ( lasso, box or circle) to select other objects some menu options that would be expected to work do not.
As I was writing this I realised it was more than one option. Initially it was the "clear parent" command, but I have noticed it also applies to "rigid body> add active/ add passive" and may apply to more but I cannot find any others right now.
Exact steps for others to reproduce the error
I will concentrate on the "alt+p" "clear parent"command as example.
from startup add a number of objects .
you can parent some objects to others but that shouldn't matter.
select any object by clicking on it (so it becomes the active object).
delete this object.
use any of the selection tools to select the other objects or just the select all command. but do not use the direct click to select.
there are now objects selected but no active object.
press alt+p to clear parent.
nothing will happen. the clear parent menu options are also greyed out.