msi installers do rush to 100% when copying files while they should progress linearilly

0.4.9-RC-35-g3eb03ef

That's a general issue for many or all MSI setups (but becomes obvious to users eyes only for larger packages like Python).

Expected behavior:
Ideally when copying files the progress bar should indicate a progress and should move nearly linearilly. When reaching 100% the copying should finish.

Observed behavior
The progress bar rushes to 100% and then the copying starts, the progress bar hangs around 100% for long time, and waits there until all copying has been performed.

Here is a sample video of Python 3.4.4 on Windows 2k3 (how it should look):
2k3properProgress_Python.webm

I guess progress-indication is only hackplemented in wine-msi.