Odd slowness in grep and dired modes

[Smith_RS]

This is for NT Emacs 24.3.1 running on Windows 7.

I found a situation where NT Emacs will slow to a crawl and consume high CPU 
cycles, the common behavior is directory browsing in dired or file browsing in 
grep-mode where the mouse-over behavior is being used. I ran the profiler and 
saw that all the time is spent in mouse-fixup-help-message.

Steps to duplicate:

- Open dired on a directory with a non trivial number of files (20 or more).
- Run the mouse over the files without selecting anything, just let the 
mouse-over behavior happen.
- Do this with profiling turned on and observe thousands of calls to 
mouse-fixup-help-message.

Alternately:

- Use grep-mode to search for a string that occurs in a large number of files.
- Continue as above.

I ran with Procmon, there is no specific I/O or registry activity during this 
slowness that I can trace.

I tried this under Linux, I see the calls to mouse-fixup-help-message but it 
doesn't jack the CPU like on Windows.

Any thoughts or ways to debug this are appreciated, as always.

Thanks.