conditional includetext and empty tocs

I need to display several sections of my document only in specific situations based on data stored in DocProperties. Currently I am doing this using the following nested field statements:

{IF {DOCPROPERTY var}="true" {INCLUDETEXT "include.docx"} ""}

This works as excepted but if there is a section headline within include.docx there will be a empty TOC entry before the actual section header. However, if I remove the if-statement and use only the plain INCLUDETEXT field the empty headline vanishes.

Example for strange includetext behaviour

I guess this is a bug so do you guys know any workaround?

Word 2016, Version 16.0.7167.2040 (most recent version available today)