Ukrainian citizens who have acquired Czech documents are increasingly trying to use them to enter the Czech Republic. Some go further - to Austria and Germany. For German and Austrian border guards, Czech and Ukrainian are all the same, but their Czech colleagues have a trained eye. It is enough to ask a couple of questions of a "Czech" (judging by the passport) to ascertain the level of his language knowledge.
It is noteworthy that the eight most recent cases of detention of Ukrainian citizens with fake Czech passports occurred not on the Czech-Ukrainian border, but on the Czech-Austrian border, i.e., during checks of individuals already leaving the country. How many of them reside within the country is unknown.
As Delovaya Praga notes, such transit "tourists" often arrive from Poland, as evidenced by border stamps in their documents. It is possible that Ukrainian citizens legally arrive in the Czech Republic with their real passports, and use the fakes to mislead Austrian and German border guards. After all, Czech citizens do not need visas to visit Austria and Germany - a passport is enough.