Showing Virtual Keyboard multiple times causes assert in jsruntime

When closing dialog containing Virtual Keyboard, the program crashes at assert in qv4runtime:
ASSERT: "value.isString()" in file
/home/ulf/dev/qt5-src/qtdeclarative/src/qml/jsruntime/qv4runtime.cpp, line 440.

Not reproducible in release mode, only debug mode.

Steps to reproduce:

• Run attached sample in debug mode
• Open Input Dialog from menu, observe virtual keyboard opening
• Open Input Dialog second time, close it after virtual keyboard is shown
• EXPECTED: Dialog properly closes
• ACTUAL: Assert is hit

If the input dialog is not destroyed (in this example via WA_DeleteOnClose) after each use, this problem is not reproducible.