There is inconsistent behavior when tabbing into the Replace field with the keyboard, such as with {Tab}. The first time you open the program and use Find-Replace and tab into the Replace field - it will select the full text so that you can easily type over it. But then when you type something new into the Replace field and open the Find-Replace panel - then everytime after that when you {Tab} into the Replace field it will not select it, meaning you have to manually delete it.
Here is a small animated GIF screencast I made with LICEcap that shows the bug:
(I am using WinXP SP3 - SublimeText 3 Build 3047.)