The PHPParser marks the interface word as error when it is used as a member variable name. The sidekick just shows "Not parsed". When I use a different name than it works and the file is parsed.
For example:
$this->interface->something = 2;
This line is valid php, so the interface word should not be marked as error and the parser should not stop at this line.
jEdit 5.1
PHPParser 2.0.2
Sidekick 1.5
java 1.7.0_45
Fixed in trunk