When a command is started, running a second command may gray
the first command you run if this second command is considered as
a "sub-command" of the first one.
This can be the case, for
instance, for contextual commands you can run from dialog boxes
to value parameters.
Therefore, as the first command is still running, its icon is
grayed out to prevent you from running it again without ending
the sub-command. As soon as the sub-command is over, the icon of
the first command is not grayed out anymore.
For instance in the Generative Shape Design
workbench, clicking Line
in the Wireframe toolbar opens the Line
Definition dalog box. In this dialog box, you have to
select points and to do so, you can run contextual commands.
When you run a contextual command, the Line icon is
grayed out and will be activated only when the contextual
command is over. The only way to cancel the Line
command without ending the contextual command is to press
Esc.