Bug in photoshop select/modify/expand command

There seems to be a weird issue with the select/modify/expand command. Any attempt to use this tool results in cutting the corners of any rectangular shape, its not rounding off the corners but adding a 45 degree  notch on every one. The same effect is not present  on the contract command . The black line shows the original selection , the red outline shows the result of select/modify/expand 50 pixels and the green shows the result of Select/modify/contract.