MultiField internally maintains its entries as a PropertysetItem, whose entry keys are integers (0-indexed), and whose values are the subfields' properties.

Currently, it calculates these integers based on count or index of its child components, which is rather fragile e.g. in case we want to have 'static' components in addition to the variable amount of subfields.

In that case, delete removes the wrong property due to mismatch between propertyIds and subfield index within the parent component.

We should carefully track what propertyId an entry is created with, and use it for deleting. In case we have to generate a new position manually, size of the itemPropertyIds collection is a better choice over componentCount.