Lightbox not coming up on double-click

I’m experiencing a strange inconsistency with the lightbox to create events through the calendar. On some computers, when the user double clicks on the calendar the lightbox comes up like expected and the user can create an event. On other computers, the user double clicks the calendar and a 5 minute event is created but no lightbox pops up. The event doesn’t save in the db, so when the refresh button is clicked the New Event disappears. I’ve tried to edit this 5 minute New Event to at least provide a work-around for my users, but the event cannot be edited.

At first, I thought this had something to do with display settings because it happened to me when I was using a projector to mirror my screen. Then I encountered 2 more computers with a single display, not connected to a project, that exhibit the same behavior.

The puzzling part is that this doesn’t happen on all computers. Has anyone encountered this situation before?

If issues occur only on some PCs, It may be related to some specific browser plugins

So far, it is the first report of such problem.