Tabs stacking works a bit weirdly. Rows of new tabs go on top of older rows. First of all in older Spark version it works vice versa and i think we should retain older style (new tabs goes to the bottom rows). And i haven't seen that new tabs go to top in any other application (browsers). Also when a new row of tabs appears it sometimes takes one tab from a previous row and puts it into a new row, though it was fitting in one row before that. And tabs which were left in the first row are stretched to fill whole row (see screenshot, two tabs are stretched). Probably this ticket should cover all these issues too. Tabs shouldnt take more space than they need.