Why is that unreasonable? Why should Jetstar bear other organisations training cost WRT the 787? It is not uncommon in the industry. The simple answer is don't accept a 787 position if you intend on leaving straight away, or accept it and pay the bond.
G.C - Actually I highly doubt you are Jetstar. More likely a QF driver - probably ex AN. This information is not new, so how did you 'Just find out'? Please stop pretending to be Jetstar and then posting drivel on this site.
If you are Jetstar then you could at least post the ENTIRE EBA for our edification.