Invalid behavior of toupper function

Entity LearningJournals has field IndividualProgramReason (enum type)

URL Request:

Unsuccessful:

/LearningJournals?$top=5&$filter=toupper(IndividualProgramReason) eq 'EDUCATION'

doesn't work 

"OData - JPA Runtime: JPA query syntax is not correct"

Successful:

/LearningJournals?$top=5&$filter=startswith(toupper(IndividualProgramReason),'EDUCATION')

/LearningJournals?$top=5&$filter=startswith(IndividualProgramReason, 'ED')

After research of problem I found:

?$filter=toupper(IndividualProgramReason) eq 'EDUCATION'

parameter EDUCATION has type String. It is conflict of type of field (enun type) and parameter (string)

?$filter=IndividualProgramReason eq 'EDUCATION'

parameter EDUCATION has type Enum. No conflict.