You have here work in progress.
There is however a bug report for that issue in egroupware.org tracker.
we look into that issue, but have been unable to reproduce the error as described.
As there is a new technology involved for displaying the messagelist grid, there was a lot of stuff changed.
Please make sure you delete cache and cookies, and recheck after that.
However there may be a bug but we could not pin it down by now.
We will check especially regarding the no-PreviewArea-active - szenario
best regards
leithoff, klaus