There is some inconsistency with cargo shuttles, supply ship designations and maintenance modules.
The basic rules as I understand them are:
It it impossible to move MSP from ship to ship without cargo shuttles.
If no ship in target fleet is designated as Supply ship, then you don't even get an option to order to "Resuply from a stationary supply ship".
If a ship is designated as Supply ship but has no cargo shuttles, then the order will be present but it will do nothing because MSP transfer is impossible.
If a maintenance fleet (with maint modules, no shuttles) has no designated supply ships, then for both maintenance and overhauls (M\O for short) the others fleets will use their own MSP supply. If they run out, then M\O stops, even if the maintenance fleet has spare MSP
If a maintenance fleet (with maint modules, no shuttles) has designated supply ships (
with no shuttles), then other fleets will use maintenance fleet's MSP for M\O
If a maintenance fleet has no designated supply ships, but a separate supply fleet with designated supply ships (
with no shuttles) happens to be in the same location, then other fleets will use supply fleet's MSP for M\O
Designation alone allows supply ship's MSP to be used for M\O of other fleets, even though MSP transfer should be impossible due to lack of shuttles.
Edit:
The ship being maintained will use up MSP from any racial populations in the same location, in descending order of MSP stockpile. If no populations are available, or have no MSP, the maintained ship will use MSP from any Supply Ships in the same location, in descending order of available MSP. Finally, if no other option is available, the maintained ship will consume its own MSP. A ship can use a combination of the above to locate sufficient MSP.
It is consistent with this logic, but still weird that loading\unloading MSP requires shuttles but M\O does not
SJW: Fixed for v1.14