I have encountered this really annoying problem in my recent campaign (I have been following the forum for a couple of weeks but I registered just for reporting this and finding solution! One the bestest games I have ever played!)
As far as I know, this IS a bug - there is no normal cause for a war to be called to end (when the claimant dies, the excommunicated ruler comes back to fold, rebelling vassal you are fighting bends the knee again to his master etc.). I have never encountered this problem in previous versions, only in 1.05c. And like the previous posters, I am HRE subject, too. I have played only one campaign with 1.05 (probably 1.05a and then updated to 1.05b) as the Count of Alcantara, whose dynasty ended as being Sultan of Andalusia but there were no problems. So, the problem is with 1.05c or HRE or both.
I started playing as the Count of Hainault (in the start vassal of Lower Lorraine, subject of HRE that is) and now I am the duke of Brabant, a direct vassal of the Kaiser. Waging independence wars ALONE against my then-liege-dukes were ok. Waging wars ALONE against other vassals (with normal, fabricated claims or De Jure claims at least) is ok. But in the second my allies answer my call to arms, I get the message that the war has ended inconclusively so I have to fight till the end all by myself. Which is kind of disturbing because I have carefully bided my time, planning my invasion, trained my troops, hired the mercs, occupied the enemies castles etc. Only positive thing is that the claims are at least pressed so they can be inherited but the next generation gets this thing, too...
Tried to resign, load and try again, the same result. There is no difference what kind of war I am waging the result is always the same if I call my allies to arms and they answer positively. Not sure if the wars end if they just reject the call because I have so many allies, there are always some who are willing to help.
I am 100& sure I am not doing anything wrong. I know the normal risks with wars (examples above). I can play otherwise normally and try to win wars alone but this makes alliances totally useless. And careful matchmaking becomes pretty useless (as far as I know, there are no other means but marriages to make war alliances in CK2). At the moment arranging marriages are only getting healthy, clever and able spouses and hoping to get interesting inheritance schemes.
I hope this thing gets fixed soon.
