Works for me with:
Build-Date: 2013-10-28 00:48:17 Revision: 6337 Is-Local-Build: true Identification: JOSM/1.5 (6337 SVN en) Windows 8 64-Bit Memory Usage: 295 MB / 1813 MB (196 MB allocated, but free) Java version: 1.7.0_40, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Is it still an issue for you ?