I have found two usecases, which are not supported by PlantUml (Version 8053) and PlantUml Pluging for Eclipse (version 1.1.8.8051 in conjuction with Eclipse Luna (4.4.1)).
1) line containing only /// symboles (line 4 in not working example) wrongly parsed by Eclipse Plugin. I get Syntax Error.
working example:
/// @startuml "Call sequence MainFunction()"
/// ENV -> CompA: MainFunction()
/// CompA -> ENV
/// @enduml
not working example:
/// @startuml "Call sequence MainFunction()"
/// ENV -> CompA: MainFunction()
/// CompA -> ENV
///
/// @enduml
2) tab(s) symbol after ///. Not working in both PlantUML and Eclipse pluging (Syntax Error)
not working example: (tab in line 3 after ///)
/// @startuml "Call sequence MainFunction()"
/// ENV -> CompA: MainFunction()
/// CompA -> ENV
/// @enduml
