Starting with version 7982, the rendering for conditions & loops in activity diagrams has been changed.
See vote on http://www.doodle.com/itu942r3atzbuy9m
You can use skinparam to change this behaviour:
@startuml
skinparam conditionStyle diamond
start
repeat
:act1;
:act2;
repeatwhile (end)
:act3;
@enduml
You can choose between :
skinparam conditionStyle diamond
skinparam conditionStyle inside
skinparam conditionStyle foo1
For "foo1", we definitively need a better idea...
Regards,