Bug description

(this template is intended for bug reports, erase it when requesting features/enhancements)

### Steps to reproduce the bug
1. go to piskelapp.com
2. select a tool
3. ...

### Environment details
* operating system:
* browser (or offline application version):

### Sprite details
* number of frames:
* sprite resolution:
* session duration:

Feel free to include a screenshot of the bug, a .piskel file of the sprite or anything else that can help us investigate.