The following snippet of code trips an error in a PHP file when the cursor is placed somewhere inside the <script> tag:
The error is obviously tripped by what the editor sees as a JavaScript syntax error.
If a manual PHP syntax check is run, no syntax error is found. That is the correct result because this is perfectly valid PHP, not an error.
Once the error is marked with the pink highlight, it remains unless another syntax error is found elsewhere in the file. If another error is found, that error is highlighted by the PHP syntax checker. Once that error is resolved, the highlight in the JS code does not return unless the cursor is again placed in the <script> tag.
This use case is quite common for me because it allows server-side results to customize the JS code that will be sent to the browser. I do it all the time.
Because the code shown above is legal PHP syntax, I consider this a serious bug.