When you block-select (Shift+Alt+Arrow keys) text from multiple lines and then paste something from the clipboard history (Ctrl+Shift+V), the pasted text will replace the selection as if it were selected non-block, e.g. replace full lines even though the lines are not fully selected. The expected behavior would be that the text retrieved from the clipboard history would replace each line in the block selection once, e.g. be replicated as many times as the block selection contains lines (for reference, see what happens when you paste in the regular way Ctrl+V when a multiline block selection is selected).
VA_X.dll file version 10.9.2212.0 built 2017.03.23 DevEnv.exe version 14.0.25420.1 Professional msenv.dll version 14.0.25431.1 Comctl32.dll version 6.10.9600.18006 Windows 8.1 6.3 Build 9600 8 processors (x86-64, WOW64) Language info: 1252, 0x40b