Lezyne pumps and tubes with removable valve cores.
Had a problem recently when I punctured. I fitted a spare (a Conti which has a removable valve core). Inflated the tyre successfully but when I removed the Lezyne connector - disaster, the core unscrewed, obviously totally deflating the tyre. Several attempts failed and I would have been stranded miles from home but luckilly I had a second spare tube with a fixed valve core. I have since heard of others who use Lezyne/removable core tube combination having the same problem. Solution is to make sure all removable valve cores are nipped up tight (a pair of pliers will do it) or avoid using removable core tubes.