However there are some weaknesses in the solution (and reasons therefore why a brand owner would continue to pursue). When it comes down to it, the trade mark itself is still problematic, and there will still be cases where the trade mark is used in the absence of the disclaimer. Also, as a brand owner I don't want to have to continue to monitor the third party user just to make sure they continue to use the disclaimer.
Also, in addition to the confusion argument, there is also the argument that absent confusion, the third party is essentially looking to free-ride on the goodwill of the brand owner. That cause of action doesn't require confusion to be proved.
It's really down to Instagram and how they want to play it. Having a settlement agreement obliging Littergram to include the disclaimer in various places at all times may be sufficient. But the fact is, Instagram hold quite a strong hand and don't need to settle for just disclaimer, nor for the above reasons would that be advisable.