To send us a ticket, visit the
www.taleworlds.com site and login to your forum account from the top right. Click to "My Account" and then click to "My Open Tickets". You can create a ticket there and include the save file and as well as the forum link of this thread. You can find more info about how to upload files to us with the new ticketing system
here.
Update : after playing again and not having the bug anymore ( for some reason ) i think i've pinpointed the problem : after playing a field battle with your army and creating control groups for cavalry and cav archers, those control groups keep exisiting in sieges with no way to remove these control groups ( even though the troops are unmounted ) causing the bug. for some reason these control groups stopped showing up in sieges today (for me).
Update 2 : after 2 sieges going as planned, the bug occured again, with no cav / cav archers control groups, so that wasn't the issue. i've reloaded the save just before starting the offensive, but this time I removed my horse before the fight ( i was commandeering my unmounted ranged troops while being on horseback myself ) and.. it seems to work, for this one siege at least, i'll try to test this again and keep you updated, high chance the bug occurs when a mounted commander leads unmounted troops. ( maybe it would even happen if a melee commander was leading ranged troops or the opposite )
Update 3 : bug occuring again whether or not i'm on horse back leading a non mounted formation. although now I have irrelevant cav and cav archers control groups forced on me in siege battles, so in the end i think the problem comes from both irrelevant control groups forced on the player AND formation leader not corresponding to the troop type, i'll leave further testing to you guys.