Runtime error on iOS when adding/removing properties of JS objects

When properties of a Javascript object are dynamically added or deleted, the application may crash on iOS with the message:
ASSERT: "to >= inlineSize && from > to" in file jsruntime/qv4internalclass.cpp, line 174

This only happens for Debug builds on iOS (both on actual devices and the simulator).

The error can be reproduced with the following use-case:

• Create a javascript object
• Add N properties (e.g. add 3 properties)
• Remove N-1 properties (e.g. remove 2 properties, no problems until here)
• Remove another property (causes the error)

Every iOS app that dynamically modifies a JS object cannot run in Debug mode anymore because of this issue. A quick workaround is to already include all possible properties in the initial JS object with 'undefined' as the property value.