A JIRA ticket has been opened for this issue (
LPS-2566), and a fix has been committed to trunk. If you wish to track its status (for example, to track when it's backported to the version of Liferay you are using), you may bookmark that URL.
To patch the issue yourself, in /portal-web/html/common/themes/top_js.jspf, you should see a line which reads:
Liferay.currentURL = '<%= currentURL %>';
Update that line to read:
Liferay.currentURL = unescape('<%= HttpUtil.encodeURL(currentURL) %>');
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