Hello Ga Que,
Thank you for contacting us.
It appears that this is an issue in the internal mnemonic processing. I have logged it in our Public Issue Tracking System
and we will address it in a future release. Here you can find the PITS item: http://www.telerik.com/support/pits.aspx#/public/winforms/12589
For the time being, you can workaround this by assigning a shortcut to the drop-down button:
Your Telerik points
have been updated for bringing this to our attention.
Do not hesitate to contact us if you have any further questions.
the Telerik team