installed 4.1 final today - and after playing music and doing stuff in the library for a while, got some really nasty bugs with crashes and message-boxes filling the screen

I think it's related to having disabled the Tabs bar, and somehow I do something to cause the standard "default" tab to appear in the tab bar even if it's disabled. However, this also then contains an 'x' to close it... If I click this X the following messages appear and I have to terminate the MM process.
"Tab Controller in TabsManager must not be nil!"
See screenshot:

Not sure how to reproduce exactly, will try some more tomorrow, or if anyone else has seen this (would surprise me if no-one else has). It seems to be related to alt-tabbing probably,
It also might be related to having two screens, since MM 4.1 seems to behave strangely when resizing/maximizing? But I think mainly this is because I have disable the tabs, since I do not like how they look, and I tend not to use tabs anyway.
Here are my system specs:
OS Name Microsoft Windows 7 Professional
Version 6.1.7601 Service Pack 1 Build 7601
System Type x64-based PC
System Model P5E64 WS EVOLUTION
Processor Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz, 2830 Mhz, 4 Core(s), 4 Logical Processor(s)
Installed Physical Memory (RAM) 8,00 GB
Name NVIDIA GeForce GTX 580
Driver Version 9.18.13.3221
Resolution 1280 x 720 x 60 hertz