This happens because the minimum width is less than the width of the buttons strip.
Created attachment 100108 [details] patch
Manually committed http://trac.webkit.org/changeset/90735 2011-07-08 Mikhail Naganov <mnaganov@chromium.org> Web Inspector: Fix resizing of sidebar pane in Timeline and Profile panels. https://bugs.webkit.org/show_bug.cgi?id=64161 Reviewed by Pavel Feldman. * inspector/front-end/ProfilesPanel.js: (WebInspector.ProfilesPanel.prototype.updateMainViewWidth): * inspector/front-end/TimelineOverviewPane.js: (WebInspector.TimelineOverviewPane.prototype.updateMainViewWidth):