My colony is under attack by cravens (Land battle) , I have a fleet in orbit

my system is under the lumeris zone of influence (witch grows very fast every turn ???? )

i cant attack the craven fleet because the Attack icon is greyed out and says: 'cant attack allied fleets'

so i cant attack the craven fleet but the cravan can invade my colony ??

NOTE: my diplomatic status with the lumeris is 'cold war' and with the craven is 'war'

because of that i have to declare war on lumeris to defende ny colony.

The war goes by and ...

In turn 136 i was at war with the craven and trying to takie back the only colony i lost to them.
I start the land battle and won a victory without killing all the enemy

in turn 137 some screen appear saying i lost the war and must pay 48 dust because i the
colony i was taking back. 
In the same turn (137) the pending battle continues and i take back the planet.

conclusion: i recover my planet and must pay the tribute all the same because the war ended !!!

why the war just ends like that ?

Not that I've personally played EA, but from what I've seen and read, it sounds like you've just encountered the new 'Force Truce' mechanic. I'd recommend reading the war GDD to understand it.

Thats what I reckon it is anyway, could be wrong.