URL with ? in it gets changed when launched from within Calendar

MacBook Pro (13-inch, Mid 2010), 2.4 GHz Intel Core 2 Duo, 16 GB 1067 MHz DDR3, Internal SSD

OSX El Capitain 10.11.3 (15D21)

Calendar Version 8.0 (2092.2), Safari Version 9.0.3 (11601.4.4), Google Chrome Version 47.0.2526.111 (64-bit)

When I cut & paste a URL which has a ? in it into Calendar from either Safari or Chrome, when I click on the link in Calendar it changes the URL by converting the ? to %3F which causes a security alert

Server Error in '/' Application.

A potentially dangerous Request.Path value was detected from the client (?).

Any suggestions?