System Information
Win7/64, GTX 750 Ti

Blender Version
2.74 official, 2.75-42314b3-win64

Short description of error
Whenever a speed control strip is based on a soft-trimmed input strip, the frame mapping is not right.

Exact steps for others to reproduce the error
Please open

Description:
The file contains two scenes named "Scene" and "Video":

• Scene "Scene" displays letters A to J. Frame range is 0 to 9 (10 frames). Letters instead of numbers have been used to avoid a 0-based/1-based confusion.
• Scene "Video" is only used for the VSE. Channel 1 contains a scene strip. The soft-trim start is 4, i.e. letters A, B, C and D have been trimmed. Consequently, 6 letters are left (E to J).

Now, the goal is to playback these 6 letters at 50% speed. This results in 12 frames with each letter being rendered twice, so the expected final sequence is EEFFGGHHIIJJ. The steps are:

1. Slide the right arrow of the strip to the right by 6 frames.
2. Add a speed control strip.

The resulting image sequence is EEFFGHHIJJJJ (Blender 2.74) or EEFGGHIIJJJJ (Build 42314b3)
The expected image sequence is EEFFGGHHIIJJ (each letter twice)

This is probably because soft trimming has not been taken into account correctly.