Upgraded to 0.7.0-dev tonight. I know it's not a stable version, but I'd been using development version previously.
Also upgraded Lavender from Github to 1.0.1 - issue occurs in both this and previous version.
Sidebars - all appear under main content area in all areas, except forum index - Recent, Tags, Popular, User, Register, Login
I've removed all HTML widgets (I have three - one with a Facebook & Twitter button, one with a Google advert and one with a link to a fundraising page) and this still has no effect.
Tried removing all widgets from Global Sidebar and using only widgets on: groups/details.tpl, home.tpl & category.tpl
This happens when I choose fixed width or 100% at bottom-right of page, both in Chrome & Firefox.
*edited to mention it's 0.7.0-dev to prevent confusion in future