Blocking refresh causing UI freeze [0.6.6]

[M4rtinK]

Using the "refresh" action from the pull up menu or the refresh cover action causes a UI freeze until the refresh is complete - which is not an insignificant amount of time in my case due to having many columns, some of which have substantial "traffic". Once the UI un-freezes Twablet is again usable without issues.

I don't think this freeze happened on previous versions, so this could be a regression introduced in 0.6.6.

[SfietKonstantin]

The fixes happens when you have lots of columns, I still need to investigate this ...