Two weeks ago, late night we were like 10 people on EU_5 or EU_2 I don't remember.
3 the_Grey guys were rocking the server. I soon found out they managed to stay together all the time. So I changed my banner to the grey order one, joined and tried doing the same thing (go to spec then join again). It works really flawlessly. I had a nice x5 for an hour or two (ty btw, even though that was a STF char).
I don't blame anyone, as the main problem is the auto-balancer's inability to measure real effectiveness. I don't consider this forced clan-stacking through spec mode nor the usage of other clan's banners as abuse. Simply because both counter each other.
Read : if you really don't want people in the same clan to stack, use their banner.