After creating a new account, actions taken on pages opened prior to account creation fail, and the info/error messages about those actions also fail. Yes, this is an edge case, but a bug nonetheless.
Step-by-step event timeline:
- A long time ago, I created accounts on Stack Overflow, Meta Stack Exchange and other SE sites, but not Travel Stack Exchange
- While logged into Meta SE, I opened several Travel SE questions in different tabs
- On one of those Travel SE tabs, I clicked the "Join this community" button at the top of the page
- I clicked the "Confirm new account" button, agreeing to the site's terms and conditions; this actually created the Travel-specific account and linked it with my existing network profile
- On the next page, I verified that the account was created, and that the 100-point association bonus appeared
- In a separate, Travel SE tab, already open from before I created the Travel SE account, I clicked a question's upvote button
- The system did not register the vote, and displayed an empty white box over part of the question (in hindsight, it looks like it was probably intended to contain the "Join this site" prompt)
I didn't see any error messages or guidance from the system on the page. I didn't think to open the inspector before refreshing, though. After refreshing the page, my new account's identicon and reputation appeared in the header, and I was able to cast a vote normally.