QMAKE_BUNDLE ignored during build

It appears a regression has happened from a fix in 5.11.2 (QTBUG-70072)

As documented in qmake-variable-reference.html#qmake-provisioning-profile, you should be able to define this in your .pro file:

QMAKE_TARGET_BUNDLE_PREFIX = com.mycompany
QMAKE_BUNDLE = appid_custom

and the resulting bundle ID would be

com.mycompany.appid_custom

Instead it becomes:

com.mycompany.${PRODUCT_NAME:rfc1034identifier}

The QMAKE_BUNDLE set in pro appears to be getting cleared (most likely changed) somewhere and as a result in ./Qt5.13/5.13.0/clang_64/mkspecs/features/mac/default_post.prf

xcode_product_bundle_target = $$QMAKE_BUNDLE  <----cleared/changed here somehow?
isEmpty(xcode_product_bundle_target): \
   xcode_product_bundle_target = ${PRODUCT_NAME:rfc1034identifier}

Also reported on original bug in comments by someone else.