[pdftex] Rebuilding pdftex gives ---! Must increase the hyph_size (Fatal format file error; I'm stymied)

[Vasile Gaburici]

I've applied a small patch (unrelated to hyphenation) to pdftex 1.40.9
sources and I've successfully recompiled it. But when I try to use it
against the TeXLive 2008 tree (without overwriting the old binary),
I'm getting this:

fmtutil: /home/vga/.texlive2008/texmf-var/web2c/pdftex/pdflatex.fmt installed.
---! Must increase the hyph_size
(Fatal format file error; I'm stymied)

Changing the hyph_size in texmf.cnf doesn's help. Any hints what could be wrong?