yes, 1.5.5 is out.
you can get it from here:
http://impagina.org/download#development(or through the official download page on scribus.net if you want to go through a few more hops... they link to the same binaries, hosted on sourceforge)
1.5.5 is not a stable version.
the next stable version will be 1.6.
but depending on whom you ask, you might get the reply that 1.5.5 is more stable than any 1.4.x version has ever been...
if you save something in 1.5.5 you should be able to open it 1.5.4 but there is no guarantee.
iirc the issue with the wandering windows has been solved.
but i fear that what i recall was fixed before 1.5.4 so if you experienced this in 1.5.4 you might need to test and if it still happens check that a ticket is still open in the bug tracker (
https://bugs.scribus.net) or open one if you can't find any.
finally, you can keep 1.5.4 and 1.5.5 on the same computer (depending on how you install it).
if you reported the bug please go to the bug tracker (
https://bugs.scribus.net)