A four-carriage train collided with a stationary eight-carriage train at Plymouth Railway Station on Sunday.
Andy Roden, from Rail Magazine, said the platform appeared to have been "too short" for both trains.
But Great Western Railway (GWR) said trains of different lengths regularly share platforms across the UK.
Police said no-one was seriously hurt in the "low impact collision", but eight casualties were taken to the city's Derriford Hospital for treatment, with two detained overnight.
Mr Roden said while there was "nothing inherently unsafe" about trains sharing platforms, it was the "first time" he had heard that a long train had shared a platform with a short train at Plymouth Railway Station.
"You would need a jolly good reason to do it", Mr Roden added.
However, a spokesman for GWR, said: "Trains of different lengths share platforms at stations safely and without incident across the UK network on a daily basis.
"Clearly something went wrong [on Sunday], and we are working with Network Rail, British Transport Police and the Rail Accident Investigation Branch to understand exactly what happened as quickly as possible."
He said it would be "wrong to speculate about the causes" and added every move by a train was risk assessed with two trains sharing a platform at Plymouth being "a permitted move".
The British Transport Police said: "At this stage we believe that a moving train drove into the back of a stationary train on platform six at the station, and we are currently looking into the circumstances to determine how this happened."
The Rail Accident Investigation Branch will lead the investigate into the crash, but no timescale has been given.
A railway expert claims it is "extremely unusual" for long and short trains to share a platform, following a crash that injured 18 people.