Description
If the name of a project is same as the key of another project, then, when using JQL to search by name on the first project would retrieve all issues from the second project.
The problem stems from mismatch between what Autocomplete fills up in the JQL, versus, what JQL search prioritizes. The Autocomplete fills up based on the project name. However, JQL search prioritizes project keys. If no project keys are found, then only it goes to search for project name.

First Symptom

Steps to reproduce
1. Create the first project with name: My Test Project, key: MTP
2. Create the second project with name MTP, key: MP
3. Seach with advance JQL:

project ="MTP"

4. All issues belong to My Test Project project are retrieved.

Expected result
All issues belong to MTP project should be retrieved.

Second Symptom

Steps to reproduce

1. create first project with name My Test Project, key: MTP
2. create second project with name MTP, key: MP
3. create a new JQL, insert:

   project=MTP
   

4. select project with key MP from the suggested list
5. hit Enter and the issue for project with key "MTP" is return

Expected Result
Issue for project with key "MP" is return as user manually select the project from the suggestion list

Workaround
Searching based on the Key, for example

project = MP