editing question

[toyL]

ok, stereo drums on 3 and 4, stereo guitar on 5 and 6, stereo guitar on 7 and 8 in CuBaseVST32 r6...with CuBase running I dbl clk on either of the two stereo guitar parts to bring up WAVELAB, insert some silence, and save...the edited parts are then updated in WAVELAB...I return to CuBase by clicking on CuBase in the tray, and CuBase automatically updates the edited parts and returns to where I started...no problem...now I go back to 5 and 6 in WAVELAB and copy most of the part and paste it onto the end of itself...I save again in WAVELAB...no problem...I bring CuBase back up, but, now it doesn't take the time to update the part and 5 and 6 do not contain my last edit from WAVELAB...very strange to me...why does CuBase update the part when I use WAVELAB to insert silence, but, not when I paste?...thanks.