Hello everyone!
I’ve been working with a definition (*.dyn file), then i’ve created a custom node with an another custom node inside. Then i had to grab some nodes from a completely another definition, thus, i opened an another *.dyn file. Dynamo asked me, if i want to save my previous definition. I’ve pressed “Yes”. Then i’ve done my operations with a new definition and closed it with no saving. Then i’ve opened my initial definition and it turned out to be overwritten with the custom-node 
The initial definition was restored by my backups. But the problem repeats again and again all the time i make such operations. Is there any way to reinstall Dynamo only (hope this helps?) or may i reinstall whole Revit?
Had someone got the same issue?
