Cannot read property tagName of undefined

[Dariusz Kubiak]

When I nest in 4 or more objects deep, ex:
Menu Items / Accounting/Journal Entries/Journal Items / Journal Items / account.move.line.tree
I get OpenERP Client Error Script error. :0
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Uncaught TypeError: Cannot read property 'tagName' of undefined onloadwff.js:338
lpIsVisible onloadwff.js:338
countFormEquivalents onloadwff.js:861
checkShouldRecheck onloadwff.js:321
(anonymous function)
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function lpIsVisible(a, b) {
Uncaught TypeError: Cannot read property 'tagName' of undefined (repeated 8 times)
    if ("INPUT" == a.tagName && "hidden" == a.type)
Uncaught TypeError: Cannot read property 'tagName' of undefined