gnome-shell adds some symbols at end of window name displayed on top panel.
For example it adds something like "9q" or "9!" (suffix changes if gnome shell or program was restarted) to window with name "NetBeans IDE 8.1". xprop says that window don't have this suffix

$ xprop
WM_STATE(WM_STATE):
		window state: Normal
		icon window: 0x0
_NET_WM_DESKTOP(CARDINAL) = 2
_NET_WM_ALLOWED_ACTIONS(ATOM) = _NET_WM_ACTION_MOVE, _NET_WM_ACTION_RESIZE, _NET_WM_ACTION_FULLSCREEN, _NET_WM_ACTION_MINIMIZE, _NET_WM_ACTION_SHADE, _NET_WM_ACTION_MAXIMIZE_HORZ, _NET_WM_ACTION_MAXIMIZE_VERT, _NET_WM_ACTION_CHANGE_DESKTOP, _NET_WM_ACTION_CLOSE, _NET_WM_ACTION_ABOVE, _NET_WM_ACTION_BELOW
_NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_NORMAL
_MOTIF_WM_HINTS(_MOTIF_WM_HINTS) = 0x3, 0x1, 0x1, 0x0, 0x0
_MOTIF_DRAG_RECEIVER_INFO(_MOTIF_DRAG_RECEIVER_INFO) = 0x6c, 0x0, 0x5, 0x0, 0x51, 0x0, 0x60, 0x2, 0x0, 0x0, 0x0, 0x0, 0x10, 0x0, 0x0, 0x0
XdndAware(ATOM) = BITMAP
_NET_FRAME_EXTENTS(CARDINAL) = 0, 0, 37, 0
_NET_WM_STATE(ATOM) = _NET_WM_STATE_MAXIMIZED_HORZ, _NET_WM_STATE_MAXIMIZED_VERT, _NET_WM_STATE_FOCUSED
WM_HINTS(WM_HINTS):
		Client accepts input or input focus: False
		Initial state is Normal State.
_NET_WM_ICON(CARDINAL) = 	Icon (16 x 16):

... skipped ...

_NET_WM_PID(CARDINAL) = 17832
WM_CLIENT_MACHINE(STRING) = "gfl-1789"
WM_PROTOCOLS(ATOM): protocols  WM_TAKE_FOCUS, WM_DELETE_WINDOW
WM_CLASS(STRING) = "sun-awt-X11-XFramePeer", "NetBeans IDE 8.1"
WM_CLIENT_LEADER(WINDOW): window id # 0x2600008
_NET_WM_ICON_NAME(UTF8_STRING) = "NetBeans IDE 8.1"
WM_ICON_NAME(STRING) = "NetBeans IDE 8.1"
_NET_WM_NAME(UTF8_STRING) = "NetBeans IDE 8.1"
WM_NAME(STRING) = "NetBeans IDE 8.1"
WM_NORMAL_HINTS(WM_SIZE_HINTS):
		user specified location: 0, 27
		program specified location: 0, 27
		program specified size: 1590 by 843
		window gravity: NorthWest

Issue reproducible with GNOME Shell 3.18.3 and NetBeans 8.1.