It seems that eclipse has always had some flaky auto-complete functionality. I'm now using Helios and still have trouble with eclipse refusing to offer auto-complete on some common tags in PHP. It's really hard to guess when the auto-complete will work as it seems to change it's mind and work on/off at it's own will.
Is there something that triggers auto-complete on/off for certain elements or features?
Unfortunately Eclipse Helios has the best auto-complete for php of any free IDE. Zend Studio for Eclipse is a lot better, but it is expensive. Zend's Debugger is also better than even the new PDT.
Is there something that triggers auto-complete on/off for certain elements or features?
I've just checked Helio, and the only one I know off of my head and so far in preferences is Template. You can trigger auto-complete with Code template and customized it. Other than that I can't seem to find a list of php syntax that would trigger it.
If it bothers you that some element aren't getting auto complete, then perhaps you can try code template?
You can try to change your PHP version in Eclipse to 5.3?
Code assist is only a pain for me when I declare classes and I assume it'll do curly braces after I declare the class, it doesn't, it tried to add interface and abstract in there before the curly braces >_>.
Apparently this is a common problem. Based on this thread I tried netbeans (OpenSource) and phpStorm ($$$) and I must admit that they both provide better code completion.
I'm guessing there is just something buggy in the PDT build for the time being that stops auto-complete from working at times. I'll have to wait a little while and come back to using it I guess.