Cannot override --context_param with Implicit Context Load

[Anonymous]

I had a job running fine using and was able to pass a command line param:
--context_param DateVisited=20160731
I just converted the job to use Implicit Context Loads from a file (which works fine) but now the command line override is being ignored (it would appear). The context being used is shared across a couple of jobs in the project and I wonder if that has anything to do with it.
In the context file I include:
DateVisited=
The job runs fine if I set the value in the context value but this is not what I want to do - it should be fine to override in the command line, what am I doing wrong?
M

[Anonymous]

The implicit context load runs as last and overrides the existing variable. You should take care your variable DateVisited is not in the context properties file you load with the implicit context load. The implicit context load does not affect variables which are not set in the loaded file.

[Anonymous]

Brilliant - I did wonder but couldn't find any docs to tell me whether that was the case.
Cheers,
M