When you paste copied code with CTRL+V, RubyMine will change the indentation of the pasted code. You can prevent this by pasting with CTRL+ALT+Shift+V instead ("Paste Simple").

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

To change this behavior entirely, you can open your settings and navigate to Editor / General / Smart Keys. Here you can select one of three options for Reformat on paste:

• None
• Indent Each Line (default)
• Indent Block
• Reformat Block

You might want to try "Indent Block".