"Use an external calendar" checkbox setting no longer sticking

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On 2 Windows computers the "Use an external calendar" checkbox setting is no longer sticking after installing the latest update to version 6.0.0(37205).  It works when I choose Outlook, but when setting up the next meeting, the checkbox is unselected and I have to select it manually each time.

Is this a bug in this version, or did the update reset some other setting that I need to set to get my "Use an external calendar" checkbox setting to stick?

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I found that unselecting "Try new version" avoids this problem.  That is on by default after the upgrade. 

Hopefully the lack of sticking of the external calendar setting will be fixed before we are forced to use the new version.