A hearty thanks goes out to Steve Stafford, who documented the solution to a problem that arose in my office yesterday, way back in 2012, in his Revit OpEd blog.
The problem is that if you use the Move tool with the Disjoin option checked, and then later in that session try to use it to move a Ceiling grid pattern or other model pattern, Revit "remembers" that the Disjoin option was selected previously, and starts out with it turned on. Since Disjoin is not applicable to moving a model pattern, Revit disables (grays out) this option when a model pattern is the object of the Move tool. You might think that since the option is disabled, that it would not have any effect on the command at hand, but you would be wrong. Having this option checked effectively breaks the command, and while you can go through the motions, no change will take place.
To add insult to injury, having the Disjoin option disabled means you cannot clear the checkmark while trying to move a model pattern. The solution, as Steve reported, is to select an object for which the Move Disjoin option is active, such as a Wall, and select the Move tool. Clear the check mark at the Disjoin option on the Options bar, and then press the ESC key twice to exit the command without actually moving the selected object. Now you cah select the Ceiling grid or other model pattern and use the Move tool to reposition the pattern.
Here is a Screencast showing both the problem and the solution, that I put together for users in my office who would rather see the solution than read about it.