I would be interested to know if you have the same issues with the provided examples that use treegrids and if so that tells me its a specific browser or device that I have not tested on that needs to be fine tuned.

Otherwise, my first guess is that it is related to possible use of itemHeight<>47 pixels (Sencha's default) and variableHeights=true. CalendarPicker uses treegrid to expand/collapse the calendars and uses this configuration to set different row heights. I found that I had to set minHeight, maxHeight and height all with !important in my css to force particular heights while scrolling. Take a look at css selector
.x-touchtreegrid-list-calendar .touchtreegrid-list-categ {...}
in categorypicker.css (./CategoryPicker/resources/css/ directory) for an example.

You can send me private message with more details of your example if this doesn't help.

Best Regards,
Steve Luken