Steps to reproduce:

1. enter into graph edit form
2. change some graph name changing for example some low case characters to upper case
3. Click update

Result:
after press update frontend reports 'Graph '<graph_name>" already exists on "<template_or_host_name>"'
Workaround:

• on change case of some characters in graph name add some new character for example at the end of the name
• go again to graph name edit form
• remove additional character(s)
• press update