I believe the difference is because the tclsh Windows build does not have the appropriate shell dialog manifest lines. 8.6.1 tclsh did not have a manifest at all afaict. In 8.6.2RC1, tclsh has a manifest but the following lines which are present in wish.exe.manifest.in are missing from tclsh.exe.manifest.in

    <asmv3:application>
	<asmv3:windowsSettings

	    <dpiAware>true</dpiAware>
	</asmv3:windowsSettings>
    </asmv3:application>
    <dependency>
	<dependentAssembly>
	    <assemblyIdentity
		    type="win32"
		    name="Microsoft.Windows.Common-Controls"


		    publicKeyToken="6595b64144ccf1df"
		    language="*"
		/>
	</dependentAssembly>
    </dependency>


Adding this to my build fixed this problem but not sure what other implications it might have. (Actually only the Common-Controls piece is relevant here but the DPI section should also be included I think)

/Ashok