That happens to me too. When you play live your attention is split up and you're in the spotlight, this makes you think about a lot of things you aren't thinking about alone, practicing.

Also, you're more 'in the moment' so that gives you less time for reflecting, remembering. The more you play with others, the easier it is to adjust to this difference and develop your 'wingin' it' skills!

This is also when notes come in REAL handy!