The Package paths field uses Ant style wildcards, which means that a double asterisk in this case will match zero or more subdirectories. So I imagine what is happening is the additional ** has found a zip file in a nested directory, and passed that to the push command.
Exact path paths should work, so if they are not then there must be a mismatch between where the files are being saved and the paths that have been entered into the Octopus Team City plugin.
You can verify the location of files with a custom script step in the build like ls %perforce_checkout_path%. This will list the files in the build log and allow you to verify that the files exist in the expected locations.