Issue with clipboard in Windows

[Miroslav Rajcic <miroslav rajcic inet hr>]

I've implemented custom clipboard handling in my program that allows me 
to push to clipboard more than one clipboard format in parallel (plain 
text format plus "text/html" plus "HTML Format" on windows etc).

My issue is that from time to time I get report from users that they can 
not paste plain text into some text editor, and when they check the 
clipboard contents it is indeed the case that only HTML formats are 
present at the time (although the code always tries to push at least 
plain text format). The issue appears randomly, I myself have managed to 
reproduce it only once a long time ago.

The logs always show the following issue:
16:37:02.616 GTK [16]: gdkproperty-win32.c:200: OpenClipboard failed: 
Access is denied.
16:37:02.626 GTK [8]: inner_clipboard_window_procedure: assertion 
`success' failed

I've attached the example of the code quite similar to what I use.
It appears as if something is locking the clipboard, but not everything, 
HTML always seems to pass through.

Additionally, the code to block the default signal handler 
(g_signal_stop_emission_by_name part) seems to cause crash in my bigger 
program so I commented it in there.

Can anyone spot the possible issue in my code?

I am using GTK 2.24.10 for Windows here (from www.gtk.org). Compiler is 
Visual Studio 2008.
Does anyone know of any relevant fixes in the newer GTK in this regards.

Also any tips on what GTK 2.24.x build for Windows you use are welcome.

TIA,
  Miroslav

Attachment: main.cpp
Description: Text document