No it isn't odd at all. This is very normal. If the file is in use at the time of the scan then it cannot be removed until the computer is rebooted and it is remove during the boot process BEFORE the program can be auto started.
Many, many infections can only be removed this way whether you are using your onboard anti-virus program or a program like MBA-M or many others. There are some programs which will only remove infections if the removal program is run in Safe Mode. This isn't odd at all. In fact I always recommend persons reboot after using a removal program like MBA-M, whether it is in the instructions or not.