"supporting but not endorsing" is a meaningless, nonsense phrase. The words are synonyms for goodness sake. The sentiment behind it is completely transgressed when you actually work to run the Sanders campaign.
I hear what you're saying but you're misunderstanding. Boston for Bernie is a grassroots organization that is SEPERATE from the Bernie Campaign, has no connection to the democratic party, and has explicitly stated that they will not endorse Hillary Clinton. When Bernie loses they will attempt to pressure him into running as an independent. Boston for Bernie is attempting to build an independent grassroots movement.
We are supporting the B4B campaign logistically. Helping them organize and make connections with other activists. a majority of the people who make up Boston for Bernie are novice organizers. We are helping them to organize (supporting) but not endorsing Bernie. Speakers from SA at the event spoke about specific issues, not Bernie Sanders (For example education and trade unions) and made sure to clearly state that capitalism is the root of the problem.
When speaking to Sanders supporters, you have to make it clear that you do not support/endorse his run for the Democratic ticket. Remember the reason you are speaking to these people is because they are looking for a new politics. You have to explain to them that Sanders cannot achieve that because he's a Democrat. You must keep your banner independent of the Democratic Party.
Our banner is independent of the Democratic party. We have made it VERY clear to everyone that we spoke to at the Bernie rally that we do not support/endorse his run for the Democratic ticket. We are critical of Bernie on many issues and we make that clear.
By setting up and running the event you've mixed your banner with Sanders, creating much confusion. Who knows how many of the people there think Socialist Alternative are Democratic party activists? How many Sanders supporters will feel you tried to deceive them and hijack Sanders' campaign for your own ends?
No one at the event was under the impression that the democratic party had anything to do with it. We tabled outside the rally and sold papers inside, all the while making it clear that we were part of SA and not part of Boston for Bernie. A handful of organizers for P4B are also in SA. Everyone involved in P4B knows who is in SA and what SA stands for/ SA's position on Bernie.