"Both Blocks" activity signup client-side bug

[alanzhu0]

Steps to reproduce

1. Sign up for a Both Blocks type activity (where you are required to attend both blocks).
2. Sign up for another activity that is not Both Blocks.

Expected behavior

1. You will be signed up for the new activity you selected, and your signup for the other block will be removed (since it was originally the Both Blocks activity).

Actual behavior

1. You are signed up for your new activity in the current block, and your signup for the other block is not removed.

Note, this is entirely client-side JS. The database is correctly updated - the signup is in fact removed. If you reload the page, you will see this. However, the JS is not correctly reflecting this.