I think the problem is that if both parties in the diplomacy screen dont offer an alliance its just one sided.  For example you may have proposed an alliance with the Iridium without getting one in return.  So if somone declares war on them or they declare war on someone else you bound by the alliance but they didnt offer you an alliance so they have no obligations if you are attacked.

The problem as I see it is that if the other player doesnt have that treaty researched than they cant offer it in exchange.  This is why I whenever I research treaties I give it to the other races immediately.

Can someone else confirm if I'm right about this?

I am actually seing the same, I have 2 allies that is not declaring war on races that declares war on me.

And I gave them the tech for alliances, but could still only select it from my side when getting the alliances setup.

Any ideas?

This looks like a bug, some futher info

I just looked under diplomatic screen, and at the main screen when I hover my mouse over my 2 allies, it only says Close, but as a subpoint: We are allies +++ 

But if I press report on the 2 factions, then I can see under relationsship that is says Allied

Also I cant ask my allies to declare war on any 3 rd party, but I can with all other races it seems