If multi-row tabs are enabled, then that property is not recommended to use, because it has limited support, may lead to misbehavior and does not persist after postback.
Requirements
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2