Did a clean install of PX 0.5 on Win2k. Installed TBE Ver.1.5.2002120701 directly from developer's web site. Found that I can't close any tabs either by clicking on a close icon or by selecting <Close tab> from the context menu.
I uninstalled this version of TBE and re-installed version 2002112301 (the last one I downloaded). It appears to work fine with PX 0.5; I didn't try Ver.1.5.2002120701 with PX 0.4
Cheers ...