Windows batch string comparison in if statement wrong?

i try to write a tiny batch file which shall react in different way dependent on a parameter. Unfortunately the "if" statement whch compares 2 strings seem not to work as expected. The code used is:

@echo off
if "%1"=="" goto Usage
echo "Parameter: %1"
IF /I "%1"=="START" {
   echo "Why the hell is %1 == Start?"
   SET Parameter=start
   goto :execute
} else if /I "%1"=="STOP" {
   SET Parameter=stop
   goto :execute
}
echo "Parameter %1% invalid"

:Usage
echo "Synapsis:"
echo "   SwitchServices Start|Stop"
goto :EOF

:execute
SET servicename=Dnscache
SET filename=Dnscache.exe
CALL :%parameter%_Service
goto :EOF

:stop_Service
echo ... stopping service ...
net stop %servicename%
if (ERRORLEVEL GTR 0) call :kill_Service
sc config %servicename% start= disabled
Service stopped.
exit /b

:kill_Service
taskkill /f /IM %filename%
exit /b

:start_Service
echo ... starting service ...
sc config %servicename% start= auto
net start %servicename%
exit /b

:EOF

The result is:

c:\Users\kollenba\Documents\Temp>KapschServices.cmd xxx
"Parameter: xxx"
"Why the hell is xxx == Start?"
... starting service ...
[SC] ChangeServiceConfig ERFOLG
Der angeforderte Dienst wurde bereits gestartet.

I do not understand why the condition

if /I "%1"=="START"

does not work as expected. Any hints?

Precondition: the batch file must be executed with administrator permissions to allow the "net start" command. Used OS: Windows 7