[Bug 48073] New: ANSI plugin window breaks in Unicode host (Synth1 / OpenMPT)

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=48073

Bug ID: 48073
           Summary: ANSI plugin window breaks in Unicode host (Synth1 /
                    OpenMPT)
           Product: Wine
           Version: 4.0.2
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: -unknown
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

An OpenMPT user has observed an issue with the Synth1 VST which does not happen
in Windows. It boils down to OpenMPT being compiled with Unicode support.
Compiling it as an ANSI application instead makes the Synth1 feature in
question work again.

Downloads:
Synth1: https://daichilab.sakura.ne.jp/softsynth/#down
OpenMPT: https://openmpt.org/download (use the 32-bit version)
Last official OpenMPT ANSI version:
https://download.openmpt.org/archive/openmpt/1.26/OpenMPT-1.26.14.00.zip

To reproduce:

Steps to reproduce:
1) Create a new module in OpenMPT.
2) Open the plugin manager ("Select" button at the bottom of the created
module's window) and add Synth1 VST.dll (or Synth1 VST64.dll if you installed
the 64-bit version of OpenMPT)
3) Click "Put in FX01" to load the plugin.
4) Click the "Edit" button next to the "Select" button to open the plugin's UI.
5) Click the "opt" button in the Synth1 UI to configure at least two sound
banks. There is one valid soundbank in the "soundbank00" folder. For the sake
of testing,  you can copy the sy1 files in that folder to e.g. "soundbank01"
and then add that folder as a second bank.
6. Next to the "opt" button is the bank switcher. Click on the text field to
open the bank switcher and try switching between the two banks by selecting
them in the treeview on the left, then choosing a patch from that bank on the
right side (another unrelated bug can be observed here: you cannot see the
patch names in Wine, wine bug 24945)

If you are using the latest OpenMPT version (Unicode), the last step should
fail and you will always stay in the bank that was already selected. With
OpenMPT 1.26, the bank switch will happen as intended. I have verified that
compiling later OpenMPT version as ANSI applications make them work as expected
as well, so I assume that there must be a bug in Wine that is related to mixing
ANSI and Unicode window classes.