We have just found a regression in 2.5.5 if using the mysql database for accounting along with GRES. There for we tagged a 2.5.6 with the fix.
You can download it from http://www.schedmd.com/#repos. This bug only exists in 2.5.5 and 2.6.0-0pre3 systems. Those running 2.6 pre releases are advised to patch there code base or just do a pull from github. A simple patch is found here https://github.com/SchedMD/slurm/commit/e5bc5e3615515ae1c023f1e7d067fa2933307467.patch. 2.5.6 also contains a patch dealing with requeuing jobs that use GRES as well. Sorry for the inconvenience. Danny