Censys expands queries to provide additional functionality. For example, the query a:zmap.io
executes a DNS lookup and expands to ip:141.212.120.90.
Your query was changed from:
tags:imaps and 993.imaps.tls.tls.certificate.parsed.signature_algorithm.name:SHA1*
to
tags:imaps AND 993.imaps.tls.tls.certificate.parsed.signature_algorithm.name:SHA1*
If this isn't what you intended, you can run your raw query without expansion.