There is an issue related to the 5.1 version of Safari. We have not tested with it. The latest version of Safari that we tested is 5.0.1 and since then we have not performed further tests. We stopped the active development of Sitefinity 3.x after SP4 and I will log this issue as a bug for fixing. I noticed that the problem did not occur if you use classic page edit mode instead of overlay.
You can set default mode to classic through the web.config
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