The following valid code is marked as invalid in the source editor. See attached screenshot. If you hover over the red underlining, the error is "Unclosed string literal".
This is Struts2 code, but according to Yann is not a problem with the Struts2 plugin (see http://www.jetbrains.net/jira/browse/STRPL-79
).
This bug has been around quite a long time, and is not a recent regression or anything.