Openra: Minelayers can't get a group order

[FRenzy-OpenRA]

Currently, if you select a group of minelayers, and want them to place the same minefield, only one minelayer will follow the order.
You have to repeat the order for each minelayer.

[CH4Code]

Didnt even know you could order a minefield with ctrl+mousebutton! great!

[MunWolf]

We are replacing the OrderManager with a MinefieldOrderGenerator that takes the actor as a parameter, I guess we are replacing the OrderManager for every MineLayer and only the last one is kept since only the one actor, could be fixed by checking if the current OrderManager is a MinefieldOrderGenerator we add the actor to that OrderManager,

Or we do something more elegant but thats the idea that came off the top of my head.