In Windows 7 and 8 status icons are hidden by default. Setting the option "Always show icon and notification" for Claws Mail icon works until the program restart. Obviously, this problem is related to the GTK bug #609622. See commit 8a9d458bafe368335d0acca2c324f878ee64463f if you do not intend to link claws against newer version of GTK.
I am not going to pull in and reproduce the complete status icon code in the plugin, so this can only be solved by upgrading GTK+ (even a later version of the 2.16 branch should do, as the report you mentioned explains).
Since our latest release for Windows is using GTK+ far newer than 2.16, I think we can close this bug report.