Selection when dragging day event

[dwknippers]

I'm submitting a ...

[x] Bug report 
[ ] Feature request
[ ] Support request => Please do not submit a support request here, please ask on https://stackoverflow.com/

Bug description / Feature request

While dragging a draggable calendar day event, the underlying hour labels will be selected.

Minimal reproduction of the problem with instructions

The issue can be reproduced by dragging the day event. So far I've only found it occurs consistently in Firefox and on some occasions in Edge or IE.
Link to Plunkr can be found here -> https://plnkr.co/edit/epTrXDDleL8L43T85Kao?p=preview

Versions

Angular: @angular/core ^5.2.0

Calendar library: ^0.24.0

Browser name and version: Firefox Quantum 59.0.3, Edge 41.16299.248.0, IE 11.309.16299.0

[dwknippers]

Issue seems to be resolved with #521.