PHP syntax highlighting breaking

See attachment for example of how it breaks (the whole file, or sometimes just big chunks of code, will turn white). Often the highlighting breaks when adding variables in a string.

Ex

echo 'lorem ipsum '.$var.' some more text';

From what I've noticed (but I can't seem to reproduce this deliberately) this will usually happen when I add a variable AFTER have written out the whole string and then add the single quotes to escape and add a variable. More often than not I have to reopen the file for it to get back to normal.