Missing Feature when applying a MSP patch

Question

We have a piece of software that's installed with Installshield, currently at version 5.0.1.

Between the version 4.9 and 5.0.0, a new Installshield Feature, REDIST, containing Redistribuables, was added to the Installshield project. The version 5.0 is delivered as a msi, which can be installed alone or upgrade an existing 4.9 installation. We're currently working on the version 5.0.1, which is delivered as a patch (.msp). The patch is a Minor Upgrade, since the Product Code is the same as in version 5.0.0. This patch can be installed at the time of the 5.0 installation, with the PATCH property on the command line.

When installing 5.0 and the 5.0.1 patch at the same time ( msiexec /i "5.0.0.msi" PATCH="5.0.1.msp" ) on an existing 4.9, the Feature REDIST is not installed (in the install log: Feature: REDIST; Installed: Absent; Request: Null; Action: Null ). The issue does not appear when the 5.0.0 and 5.0.1 are installed separately.

I don't have much experience with Installshield, so I think I'm missing something obvious here.