The 29-year-old singer was the final founder member to leave the group in 2009 - when she was performing with Heidi Range and Amelle Berrabah - and says she ''gave up'' as the band were nothing like the one she first joined with Mutya Buena and Siobhan Donaghy, who left in 2006 and 2001 respectively.
Keisha - who was replaced in Sugababes by Jade Ewen - said: ''We had a lot of success when Mutya was in the group, but I sensed she wasn't always happy so I couldn't really enjoy that period.
''There were a few tracks I liked, but it felt like we'd lost the essence of what we were as a group. By the end, I was the only one fighting for creative control and eventually I gave up.''
The original group reformed in 2010 as Mutya Keisha Siobhan - aka MKS - and are hopeful they won't have the same problems as they did in their early days because they are no longer open to outside influence.
Speaking of their past struggles, Mutya said: ''It was [because] we were 15, 16 years old and didn't communicate.
''When you have adults around you who stir things up by taking one girl aside and telling her one thing and another something else, it creates tension.''
Keisha added to Britain's Grazia magazine: ''We were like lab rats. We had a strange relationship but it was influenced by the people around us.''
Corgan took to Instagram to confirm rumours of new Pumpkins material, saying the first songs could arrive as early as May.