It is probably necessary to change the window size to see the two behaviors described. 1) Text will fall outside the right margin. 2) the size of the right margin will change. The behaviors are triggered the application of margin-left or padding-left to the elements, though the test.xhtml only includes padding-left. Margin-right or padding-right are fine. The only styles applied are "body {border: 1px solid rgb(255, 0, 0);}" and ".message {padding-left: 2em;}". "adding "word-wrap: break-word;" to the body had no effect. I've checked this in the lasted nightly, but it also exists in Safari 2.0.4. Firefox 2.0.0.6 does not exhibit this behavior. This might be related to #14826.
Created attachment 16077 [details] testcase xhtml
Created attachment 16078 [details] odd margin + text outside margin, webkit nightly
Created attachment 16079 [details] normal margin + text outside margin, webkit nightly
Created attachment 16080 [details] test in Camino nightly
Still exists, even with webkit-svn-r95145 on SL or Lion.
Created attachment 207673 [details] Patch
Comment on attachment 207673 [details] Patch Attachment 207673 [details] did not pass mac-ews (mac): Output: http://webkit-queues.appspot.com/results/1283547 New failing tests: editing/selection/leak-document-with-selection-inside.html css2.1/t100801-c42-ibx-ht-00-d-a.html fast/writing-mode/border-radius-clipping-vertical-lr.html
Created attachment 207701 [details] Archive of layout-test-results from webkit-ews-04 for mac-mountainlion The attached test failures were seen while running run-webkit-tests on the mac-ews. Bot: webkit-ews-04 Port: mac-mountainlion Platform: Mac OS X 10.8.4
Comment on attachment 207673 [details] Patch Attachment 207673 [details] did not pass mac-wk2-ews (mac-wk2): Output: http://webkit-queues.appspot.com/results/1297236 New failing tests: css2.1/t100801-c42-ibx-ht-00-d-a.html fast/writing-mode/border-radius-clipping-vertical-lr.html
Created attachment 207718 [details] Archive of layout-test-results from webkit-ews-10 for mac-mountainlion-wk2 The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews. Bot: webkit-ews-10 Port: mac-mountainlion-wk2 Platform: Mac OS X 10.8.4
Created attachment 207759 [details] Patch
Comment on attachment 207759 [details] Patch Attachment 207759 [details] did not pass mac-wk2-ews (mac-wk2): Output: http://webkit-queues.appspot.com/results/1293475 New failing tests: fast/borders/rtl-border-03.html fast/borders/rtl-border-01.html fast/borders/rtl-border-04.html fast/writing-mode/border-radius-clipping-vertical-lr.html fast/borders/rtl-border-02.html
Created attachment 207780 [details] Archive of layout-test-results from webkit-ews-11 for mac-mountainlion-wk2 The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews. Bot: webkit-ews-11 Port: mac-mountainlion-wk2 Platform: Mac OS X 10.8.4
Comment on attachment 207759 [details] Patch Attachment 207759 [details] did not pass mac-ews (mac): Output: http://webkit-queues.appspot.com/results/1289603 New failing tests: fast/borders/rtl-border-03.html fast/borders/rtl-border-01.html fast/borders/rtl-border-04.html fast/writing-mode/border-radius-clipping-vertical-lr.html fast/borders/rtl-border-02.html
Created attachment 207797 [details] Archive of layout-test-results from webkit-ews-06 for mac-mountainlion The attached test failures were seen while running run-webkit-tests on the mac-ews. Bot: webkit-ews-06 Port: mac-mountainlion Platform: Mac OS X 10.8.4
Safari, Chrome, and Firefox all produce identical results on these test cases. I do not believe there are any remaining compatibility concerns here.