wood will absorb moisture from the back as well as the front..
its common knowledge you just dont stick plaster straight onto wood end of, even if it aint caused problems in a week or two it will eventually and the question will be asked 'who plastered this? onto wood? surely not a plasterer?
nothing to stop people using 15mm or even 1/2" board as a SUBSTITUTE for timber, specially in boxing in situations...easier to cut/work with and when stiffened up down the external corners just as strong (if not stronger) than some of the pathetic bits of hardboard ive seen people use...(they even use plasterboard to make WALLS out of Â

)
if its already there in place, board over it...
the only exceptions i can think of are timber wall plates..(exmet prior to backing) and timber lintels (old buildings, again exmet prior to backing...preferably bridging the timber)
good example might be scraping plaster off door liners...comes off easy with no damage to the door liner....try getting it off board...or render....or hardwall...
btw if you ever DO plaster over wood...dont, ffs, tell anyone.. :
