I’m using MyEclipse 3.8.4+QF2 on Eclipse 3.0.2. I was validating a JSP manually by right clicking on it and selecting “Validate JSP”. It had an error. I fixed the error, and also realized that I has mispelled the JSP itself. So I right clicked on it, and renamed the JSP file. The error message from the first validation correctly reflected the new file name. I re-validated the JSP and it succeeded (gave me the little popup with success message). However, the error message did not clear and the line with the original error was still shown in error in the JSP (red icon in the left margin).
To clear up the error message, I had to rename the file back to its old name, validate it again (which cleared the error message), then rename it back to the new name.