Homing Joints

How are your drives/motors set up?
Do you have separate drives/motors for each side?

Parallel port?
Mesa board?
Pico board?
Are the driver inputs separate for each drive?

You should have posted that on the first post.
Not being able to jog until the machine is homed when using tandem axis is a safety feature to prevent from raking the gantry.
If you try to jog with the machine not homed, only a single motor will move as it is still in Joint mode.
Probably there is a way to turn that off, but i never used it as i home the machines every time they are powered on and to prevent users from bending the expensive aluminium gantry.

Joint mode is any motor/drive/joint is controlled as such, a single motor drive that drives a single linear or angular joint.
Axis are used in World mode, and in LinuxCNC that can be a single motor/drive or up to several motor/drives, that are all controlled as a single axis.
LinuxCNC, can control 9 axis (XYZABCUVW) and each of those can have 1 to 8 motors/drives/joints, if i am not mistaken.
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From experience, this has been a magnificent addition to LinuxCNC, as it can be use to square that gantry every time the machine is homed, so even if the machine is not perfectly square or homing sensors are not perfectly aligned, the software can take care of that.

Ooops, forgot to mention, the joints/axis with a single drive/motor can be jogged before homing.
So your Z should jog.
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If you do need the machine to jog before homing and you do not need squaring the gantry, you can wire two drives on the same output on the Mesa. Also make a new config with only XYZ axis.