can't move transactions

[Jack]

I need to transfer some shares of two stocks from one investment  
account to another (same institution.)  I'm pretty sure I've done this  
in the past by creating two "remove shares" transactions, then  
duplicating them, moving the duplicates to the other account, and then  
changing those to "add shares."  Now, when I select both transactions,  
"Move to" is disabled.  Selecting just one of the transactions, the  
"move transaction to ..." pops up the "Select Account" dialog, which  
shows "Asset Accounts" but with no other accounts listed.  Shouldn't it  
be possible to transfer such transactions from one Investment Account  
to another?