It can't find my files

[Bob Howlett]

This has been driving me crazy for the last couple of hours.
I have a macro file called tutmac.tex, which I placed in
c:\fptex\texmf-local\pdftex\plain
Having duly run mktexlsr, and observed that tutmac.tex is
listed in the ls-R file in c:\fptex\texmf-local, I was
disappointed when pdftex couldn't find it. So I tried
kpsewhich tutmac.tex
and, sure enough, kpsewhich couldn't find it either.
After considerable experimenting I have found that if
I rename the above directory to
c:\fptex\texmf-local\tex\plain
and run mktexlsr again then kpsewhich finds tutmac.tex.
This behavious has me baffled. Can anyone explain it?

Bob Howlett

P.S. 
fptex 0.4, Windows98