System Information
Win8.1 64bit | GTX680
Blender Version
Broken: 2.75.2 909fa34
Worked: 2.74 offical release
Short description of error
It seems the VSE mask modifier uses "local time" for mask animation, which causes "delay" in attached case.
Exact steps for others to reproduce the error
Please see attachment, to compare it between 2.75 and 2.74. Thanks.