JS error on show/hide toolbar

Steps to Reproduce

run a page with a spreadsheet
e.g.: http://server:port/keikai-demo/excel_like

execute the following JS in the console:

ss = zk.$('@spreadsheet')
ss.setShowToolbar(false);

Current Result

zss.wpd:457 Uncaught TypeError: w.isVisible is not a function
    at b.showToolbar (zss.wpd:457)
    at b.setShowToolbar (zk.wpd:236)
    at <anonymous>:1:4

Expected Result

no error

Debug Information

Workaround