Hello @edadamo! Welcome to Ext.NET forums!
And, no, that's not a known issue. The closest to a flicker I can see in the calendar's month view is, when I hover the mouse over, it changes the tint of the hovered event to a lighter color, but thats just a color highlight, intentional color change.
Besides, latest Ext.NET version would be 4.2.2 as of now, so you're a little outdated there. Should consider upgrading. Soon, 4.3.0, based on ExtJS 6.5.0 will be out as well.
But anyway, although several changes on the ExtJS side could have (in potential) fix the issue you're facing, no direct considerable changes have been made directly to the calendar component since 4.1.0.
Best way for us to help you with such an issue would be the ability to reproduce it in our side. For that point, we have a couple forum threads that provide guidelines for this.
In this thread, you have some templates for the test case code samples: More Information Required
This one gives some ideas on simplifying a real-world test case down to an Ext.NET-specific issue test case: Tips for creating simplified code samples
We don't want your proprietary code, in fact, it just makes it harder for us to get what matters: the reported bug in Ext.NET. That's why the simplified test case, with no unrelated code, is important.
And last, a good starting point to build your issue reproducing problem would be: https://examples4.ext.net/#/Calendar/Overview/Basic/
You can also clone the whole Examples Explorer project from github
(there's also the MVC one
)and use it as base to derive test cases.
Well, I hope this helps!