Unlike other Paradox titles, units return instantly to the center of a province to restart their march from its beginning, if one accidently reclicks the active movement tasks. That is so annoying, especially regarding those looong (of course tasting quite realistic) marches, units have to make. Sometimes I want to get sure, several units from different provinces head for the same place. If some are already on their way, wire framing and issuing them all with the same task is not a good idea. Units that already marched lose all their progress and start new. 
o
It gets worse: 1st Legion marches into the next province A. As it is on its way, events occur making you wanting the Legion marching one province further into B. Normally you would just movement click into the new finnish in B. Now you shouldnt because even if their path crosses the province A your soldiers are actually heading for, they restart their movement.
So you have to wait until they arrive at A before you order them to move to B. Unfortunately the game doesnt tell you about that, so you must notice for yourself. Although this is not too bad, because there mostly isnt much to do other stuff anyway...
o It gets worse: 1st Legion marches into the next province A. As it is on its way, events occur making you wanting the Legion marching one province further into B. Normally you would just movement click into the new finnish in B. Now you shouldnt because even if their path crosses the province A your soldiers are actually heading for, they restart their movement.
So you have to wait until they arrive at A before you order them to move to B. Unfortunately the game doesnt tell you about that, so you must notice for yourself. Although this is not too bad, because there mostly isnt much to do other stuff anyway...
