Each measurement object (e.g. line, circle etc..) can be changed only once after it is created. It doesn't matter, if the object is changed right after it is created or if it is selected laster. Even saving the project and reloading it doesn't work.

Example:
Load Image
Open Measurement Module and create a line
Move one end of the line to a different place

After that no further end can be moved, neither the one moved the first time nor the second one.

Used installer version:
MITK-2012.02.99_r7146bd-win32