Windows does not allow pinning shortcuts/programs to the taskbar that contain certain words. From the MSDN article Application User Model IDs (AppUserModelIDs):
If any of the following strings, regardless of case, are included in the shortcut name, the program is not pinnable and is not displayed in the most frequently used list:
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You can work around this by first creating a shortcut to isdev.exe (do not include any of the above words in the shortcut name). This shortcut can then be pinned to the taskbar.
Josh Stechnij - Software Engineer - Flexera Software: InstallShield Team