i have no qualms training in another good dojo, but i've heard that some dojos/organisations are very political and will forbid their students to train anywhere else.
having a strong attachment to my previous dojo, i would obviously love to drop by once in a while, and attend the occasional national seminars/gasshukus when possible.
In my opinion, there's a difference between exploring other aikido styles through seminars or the occasional visit to a differnt dojo on the one hand and actually training in another dojo on the other. I have little understanding for dojos forbidding the former, but I do have some sympathy for dojos forbidding the latter. When you join a dojo, you're expected to conform to their style. (In due time, of course, you can't just flip a switch to switch styles.) Training in another dojo with a different style or regularly returning to your previous dojo, is not the best way to confirm your membership of the new dojo.