I was playing a little bit with the Facebook connect functionality and the XFBML and I got a strange error, every time that the API XFBML loaded the first time (Apache header 200), it did renders properly the fb-login button, but whenever it was being brought from the cache (Apache header 304) it did not render the button at all.
It did take me a lot of testing to get to this conclusion, and even to confirm if it was a javascript load time issue, I had it wrap up in a JQuery $(document).ready function so it would load properly. This did improve the issue (by 50%) but it did not solve it.
The solution found was to create my own FB login button and functionality (thx Rob) using the Facebook js functionality. Basically the script, under a FB.ensureInit function, will check if the user is connected and if so, redirect, otherwise it will check for the status (FB.ConnectState) and create a button based on that (login or logout).
Pasting the code here would not make much sense since it is very specific to the application, but the workaround concept is basically the same.
Have fun!!!
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