I noticed two things that may have caused problems:
When I first started sublimetext, even though I had a PHP file open it was initially set to HTML mode- changing it to PHP kept resetting it to HTML. I had fixed this by closing and reopening the program, and clearing out some user settings- I had quotes around a setting that probably didn't need them.
Also, I had a doc block that wasn't registering as being inside of a <?php ?> tag set, it was missing a space after <?php
After a bit of frustration, it seems to be working well enough.
Another side note that this wasn't really normal behavior: Hitting tab would move the cursor to a random location on the page- after hitting tab 3 or 4 times, though, it would return to its original location and start inserting 4 spaces as usual.
Everything seems to be back to normal though