User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.157 Safari/537.36 Steps to reproduce: Since updating to 38.2.0 (and Lightning integrated in Thunderbird) at seemingly random times my Calendar is switched off. I then have to go to Calendar Tab->Edit->Calendar Properties to switch is back on. In addition, on the Calendar Tab/page, frequently (though not always) the calendar in question is unchecked (and the yellow alert triangle says the calendar is momentarily not available (though it clearly is). This is on two different laptops, running Win 8.1PRO and Win7 respectively. Note that this happens almost 100% of the time after the laptop has been hibernated or put to sleep w/ Thunderbird open (but that always used to work) - but that is not the only condition under which it fails. BTW, I am connecting to an Oracle Zimbra Calendar as the server, which is also no change from previous conditions. Expected results: I expect that the calendar will stay enabled unless I choose to disable it.

This is a known issue and will be fixed with the next Lightning release.