Strange error when resizing MEMORY_TARGET

I am running into the most stupefying error. The version is 11.2.0.3.3, OS is solaris 11, in a local zone. The zone has 72G of RAM and 72G of swap allocated. The memory parameters are:

memory_max_target = 20G
memory_target = 7G
shared_pool_size = 1G

I need to *grow* the memory_target to 16G. This should be possible, as the database is already running and has pre-allocated the 20G (as far as I can see).

I execute:

SQL> alter system set memory_target = 16G;

and receive error:

ORA-02097: parameter cannot be modified because specified value is invalid ORA-00846: could not shrink MEMORY_TARGET to specified value.

What baffles me is that Oracle seems to think that *growing* the memory target from 7G to 16G involves *shrinking* it. Has anyone seen this before and found an explanation? I cannot bounce this 24/7 database to change the memory target size, is there a work-around?

Cheers,
Tony

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