Very funny,

i do almost the same:
reimp -d libmysql.lib
dlltool -k --input-def libmysql.def --dllname libmysql.dll --output-lib libmysql.a

and than in $qtdir\src\plugins\sqldrivers\mysql
qmake -o Makefile "INCLUDEPATH+=C:\MYSQL\INCLUDE" "LIBS+=-LC:\MYSQL\LIB\OPT -lmysql" mysql.pro
make

and it always worked till now. This time i used the latest mysql version 5.0.41. Maybe it's "too fresh"?

I'll check your solution!
Bye