That is the expected behavior.
eVars persist whereas props do not. Occurrences counts the number of times a given value was set, plus the number of page views for which it persisted. Reference: Occurrences
Consider this example:
Page view A: prop and evar set
Page view B
Page view C
Page view A: prop and evar set
In this case, the prop would have two occurrences because it was set twice, and they don't persist. For the eVar, it would have 4 occurrences. It was set twice on the A page views, however during page views B and C the eVar persisted, with the value that was set during the first page view.