To reproduce - first way:

1. Edit a page in text mode or in WYSIWIG mode (not the in place mode)
2. Focus the title input
3. Hit enter

To reproduce - second way:

1. In Confluence Migrator Pro, create a new migration
2. Focus any migration setting field
3. Hit enter

This probably reproduces in any page with editable property fields. It doesn't reproduce with a simple text input inserted using the html macro. 

Expected

Not sure. Probably save and view for fields in a page, probably for the title too. Definitely not the hamburger content menu to open.

Actual

The hamburger menu opens.