So this is not a bug. It would be an enhancement.
To me this declared but not implemented feature. What the point in "Find in Project Files" if it is just an another (and misleading!) name for "Find in Files"?
"Find in Project Files" can be easily implemented by passing few more options to `grep`: `--exclude` (once for every ignored file pattern) and `--exclude-dir` (once for every ignored dir pattern).