@crueegg Hi, unfortunately, we had to cope with the same issue. The only way to circumvent it was to create a singleton class that handles a mapping between the id of the QMetaType and the custom alias. See https://gitlab.inria.fr/dtk/dtk-core/-/issues/30 for more details. Thib.

I faced the same behavior, which was unexpected and undocumented. I was debugging Qt, and at the end there is the following fallback in their code. int registerHelper() const { if (d_ptr) { if (int id = d_ptr->typeId.loadRelaxed()) return id; return registerHelper(d_ptr); } return 0; } int QMetaType::registerHelper(const QtPrivate::QMetaTypeInterface *iface) { Q_ASSERT(iface); auto reg = customTypeRegistry(); if (reg) { return reg->registerCustomType(iface); } return 0; } qtbase\src\corelib\kernel\qmetatype.cpp

I have created a bug report regarding this. I used the minimal example that you have created in the bug report. Thanks for sharing your minimal example. https://bugreports.qt.io/browse/QTBUG-111968

If memory serves well, the version with a QString parameter is geared toward declaring aliases.

Thanks a lot @SGaist

Ah, okay, so it's just me being dense.